Immunolocalization of intermediate filaments in the kidney of the dromedary camel (Camelus dromedarius)

Abstract

Intermediate filaments belong to a large family of proteins which contribute to the formation of the cytoskeleton. The immunolocalization of cytoskeletal proteins has been used extensively in the diagnosis of various renal pathologies. The present study described the immunolocalization of the cytoskeletal proteins vimentin, desmin, smooth muscle actin, and cytokeratin 19 in the normal kidney of the dromedary camel. Kidney samples from eight adult camels were processed for histology and immunohistochemistry. The kidney was enclosed in a renal capsule composed of vimentin immunoreactive fibroblasts and smooth muscle actin immunoreactive smooth muscle cells. The smooth muscle cells in the renal capsule did not exhibit desmin immunoreactivity. Podocytes forming the visceral layer of the glomerular capsule were immunoreactive for vimentin. Immunoreactivity for vimentin and smooth muscle actin in the parietal layer of the glomerular capsule varied, with both reactive and non-reactive cells observed. Intraglomerular mesangial cells were immunoreactive for smooth muscle actin and desmin, but non-reactive to vimentin. The endothelial lining of blood vessels was vimentin immunoreactive, while smooth muscle actin and desmin were demonstrated in the smooth muscle cells of the vessels. The thin limbs of the loops of Henle in cortical nephrons displayed vimentin immunoreactivity. The proximal and distal convoluted tubules, as well as the collecting ducts were negative to vimentin, smooth muscle actin, desmin and cytokeratin 19 immunostaining. In conclusion, the present study has revealed that similarities and differences exist in the immunolocalization of cytoskeletal proteins in the camel when compared to other mammals. The presence of smooth muscle actin in the parietal cells of the glomerular capsule suggests a contractile function of these cells. The results of the study indicate that vimentin and smooth muscle actin can be used as markers for the identification of podocytes and intraglomerular mesangial cells, respectively, in the camel kidney.

Full text

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ORIGINAL ARTICLE Eur J Anat, 26 (4): 387-397 (2022)
Immunolocalization of intermediate
laments in the kidney of the dromedary
camel (Camelus dromedarius)
Lemiaa Eissa1, Mortada M.O. Elhassan1, Rasha B. Yaseen1, Hassan A. Ali2, Haider I. Ismail1, M.-C.
Madekurozwa3
1 Department of Anatomy, College of Veterinary Medicine, University of Bahri, Khartoum, Sudan
2 Department of Biomedical Sciences, College of Veterinary Medicine, Sudan University of Science and Technology, Khartoum, Sudan
3 Department of Anatomy and Physiology, Faculty of Veterinary Science, University of Pretoria, Pretoria, South Africa
SUMMARY
Intermediate laments belong to a large family
of proteins which contribute to the formation of
the cytoskeleton. The immunolocalization of
cytoskeletal proteins has been used extensively
in the diagnosis of various renal pathologies. The
present study described the immunolocalization
of the cytoskeletal proteins vimentin, desmin,
smooth muscle actin, and cytokeratin 19 in the
normal kidney of the dromedary camel. Kidney
samples from eight adult camels were processed
for histology and immunohistochemistry. The
kidney was enclosed in a renal capsule composed
of vimentin immunoreactive broblasts and
smooth muscle actin immunoreactive smooth
muscle cells. The smooth muscle cells in the renal
capsule did not exhibit desmin immunoreactivity.
Podocytes forming the visceral layer of the
glomerular capsule were immunoreactive for
vimentin. Immunoreactivity for vimentin and
smooth muscle actin in the parietal layer of the
glomerular capsule varied, with both reactive
and non-reactive cells observed. Intraglomerular
mesangial cells were immunoreactive for smooth
muscle actin and desmin, but non-reactive to
vimentin. The endothelial lining of blood vessels
was vimentin immunoreactive, while smooth
muscle actin and desmin were demonstrated in
the smooth muscle cells of the vessels. The thin
limbs of the loops of Henle in cortical nephrons
displayed vimentin immunoreactivity. The
proximal and distal convoluted tubules, as well
as the collecting ducts were negative to vimentin,
smooth muscle actin, desmin and cytokeratin 19
immunostaining. In conclusion, the present study
has revealed that similarities and differences exist
in the immunolocalization of cytoskeletal proteins
in the camel when compared to other mammals.
The presence of smooth muscle actin in the
parietal cells of the glomerular capsule suggests
a contractile function of these cells. The results
of the study indicate that vimentin and smooth
muscle actin can be used as markers for the
identication of podocytes and intraglomerular
mesangial cells, respectively, in the camel kidney.
Key words: Immunohistochemistry – Vimentin
– Desmin – Smooth muscle actin – Cytokeratin 19
– Camelid
Corresponding author:
Mortada M.O. Elhassan. College of Veterinary Medicine, University of
Bahri, P.O. Box 1660, Khartoum, Sudan. Phone: 0024991449. E-mail:
mortadamahgoub@bahri.edu.sd
Submitted: January 19, 2022. Accepted: March 17, 2022
https://doi.org/10.52083/ODPI9847

Intermediate laments in camel kidney
388
INTRODUCTION
Camels exist in arid and semi-arid environ-
ments, and are well-equipped with mechanisms
which allow them to withstand sub-optimal envi-
ronmental conditions, such as limited water re-
sources (Drosa et al., 2011(. One of these mech-
anisms, which is the maintenance of electrolyte
and water balance during dehydration and fast
rehydration, is attributed to the kidney (Jararr
and Faye, 2015). For a better understanding of
this renal mechanism, several investigations
have been carried out on the histology of the kid-
ney in the dromedary camel (Abdalla and Abdalla,
1979; Safer et al., 1988; Eissa et al., 2018; Eissa et
al., 2019, Abdalla, 2020). However, despite these
studies, several histological features of the camel
kidney remain unknown.
Intermediate laments form a large family of
proteins that contribute to the formation of most
of the cytoskeleton (Block et al., 2015; Lowery et
al., 2015). More than 50 different intermediate
lament proteins have been identied (Cooper
and Hausman, 2006). A knowledge of the various
types of these proteins is useful in comparing
and contrasting their structural and functional
properties. In this respect, it is widely accepted
that the main functions of intermediate laments
are related to the support of cellular physiological
activities and structural integrity (Satelli and Li,
2011; Chernoivanenko et al., 2015; Lowery et al.,
2015; Snider, 2016). Intermediate laments can
also improve the resistance of cells to various
forms of stress and damage caused by pathological
processes (Toivola et al., 2010; Battaglia et al.,
2017).
Vimentin, desmin, smooth muscle actin and
cytokeratin 19 are cytoskeletal proteins which
are present in the kidneys of several mammalian
species (Şen et al., 2010; Novakovic et al.,
2012; Laszczyńska et al., 2012). However, their
expression and distribution vary depending
on the species and type of renal epithelial cell
concerned (Şen et al., 2010). Vimentin is a specic
marker for cells of mesenchymal origin (Yang et
al., 2019). Smooth muscle actin and desmin have
been used as markers for muscle differentiation
(Rangdaeng and Truong, 1991). Desmin is found
in all muscle types (Robson et al., 2004; Lowery et
al., 2015), while smooth muscle actin is restricted
to smooth muscle cells, pericytes, myoepithelial
cells and myobroblasts (Rangdaeng and Truong,
1991). Cytokeratins are considered the most
abundant cytoskeletal components, with an
extensive localization in epithelial cells of the
kidney, liver, and lung (Bragulla and Homberger,
2009; Pastuszak et al., 2015; Djudjaj et al., 2016;
Werner et al., 2020).
Several researchers have studied cytoskeletal
proteins in normal and pathological kidneys of
humans (Şen et al., 2010; Sharma et al., 2019),
rats (Herrmann, et al., 2012; Funk, et al., 2016),
dogs (Gil da Costa et al., 2011), and polar foxes
(Laszczyńska, et al., 2012). These studies have
shown that the expression and distribution of
intermediate laments varies depending on the
type of renal cell, the pathological condition, as
well as the animal species concerned (Şen et
al., 2010; Laszczyńska et al., 2012). Due to the
lack of information on the immunolocalization
of cytoskeletal proteins in the normal camelid
kidney, the current study investigated the
distribution of vimentin, desmin, smooth muscle
actin, and cytokeratin 19 in the kidney of the one-
humped camel. It is envisaged that the information
provided in this study on the normal camelid
kidney could form a baseline for the diagnosis of
pathological renal lesions in the camel.
MATERIAL AND METHODS
Animals and tissues sampling
Eight non-pregnant female adult camels, aged
between 7 and 10 years and weighing 300 to 350
kg, were used in this study. Animals were slaugh-
tered at Assalam abattoir, Khartoum, Sudan. The
purpose of slaughtering animals was to provide
meat intended for human consumption. A total of
120 tissue samples were selected from the right
kidneys of the animals. The right kidney was tak-
en because it was reached without much delay
after the abdominal cavity being opened during
slaughtering process. Fifteen samples were taken
from each kidney (5 samples from the cortex, out-
er medulla, and inner medulla). All procedures in
this study were approved by the College Research
Board, College of Veterinary Medicine, University
of Bahri, Khartoum, Sudan.

Lemiaa Eissa et al.
389
Histological and immunohistochemical staining
Tissue samples were xed in 10% neutral
buffered formalin for ve days. Specimens were
then processed for routine histological techniques
and embedded in parafn wax. For a general
histological overview, sections of 5 µm thickness
were stained with hematoxylin and eosin.
The immunostaining technique was performed
on additional 5 µm thick sections using a
Biogenex super sensitive one-step polymer-HRP
detection system kit (Emergo Europe, The Hague,
The Netherlands). Sections were deparafnized
and endogenous peroxidase activity was blocked,
using 3% (v/v) hydrogen peroxide solution in water
for 5 min. The slides were then rinsed in a 0.01
M phosphate buffered saline solution (PBS, pH
7.4) for 5 min. For antigen retrieval, the sections
selected for desmin, smooth muscle actin and
vimentin immunostaining were microwaved at
750 W for three cycles of 7 min each. After being
allowed to cool for 20 min the sections were
rinsed in PBS. The sections for cytokeratin 19
immunostaining were incubated with Proteinase
K (Dakocytomation, Glostrup, Denmark) in 0.05
mol/L Tris-HCl (pH 7.6) solution for 3 min.
The sections were incubated at room
temperature with anti-cytokeratin 19, desmin,
smooth muscle actin or vimentin antisera. After
incubation with primary antibodies the slides
were rinsed in PBS and then incubated with the
one-step polymer-HRP reagent (Emergo Europe,
The Hague, Netherlands). Slides were then rinsed
in PBS and antibodies were visualized by addition
of a 3,3’-diaminobenzidine tetrachloride solution
(Emergo Europe, The Hague, The Netherlands).
The sections were counterstained with Mayer’s
haematoxylin. Table 1 shows the type, source, and
dilution of the primary and secondary antibodies
used in this study.
The immunostained, and haematoxylin and
eosin-stained sections were viewed using a light
microscope (Olympus BX63-Japan) connected
to a digital camera (OlympusDP72). Images were
then captured using the Cell Sens 510 software
program.
Assessment of the immunostaining intensity
Three experienced examiners participated in
the semiquantitative assessment of immunohis-
tochemical reactivity independently. Previously,
they agreed on the immunostaining intensities
being qualied as strong (+++), moderate (++),
weak (+) or negative (-).
For negative controls, the primary antibodies
utilized in this study were replaced with mouse
IgG1 (Dakocytomation, Glostrup, Denmark) which
was diluted to the same concentration as the
primary antibodies. Smooth muscle was used as
a positive control for desmin and smooth muscle
actin, while tonsillar tissue was used as a positive
control for vimentin. Skin was used as a positive
control for cytokeratin 19. No background staining
was detected in the negative control sections. The
variations in the immunostaining of sections used
in this study were minor.
Table 1. Source and dilutions of primary antibodies used in the immunohistochemical technique.
Product name Source and code Type of antibody Dilution Incubation time
Monoclonal Mouse Anti-
Vimentin
Dakocytomation, Glostrup,
Denmark, code M7020
Monoclonal Primary
Antibodies
1:200 1 hour
Monoclonal Mouse Anti-
Human Smooth Muscle Actin
Dakocytomation, Glostrup,
Denmark, code M0851
Monoclonal Primary
Antibodies
1:50 1 hour
Monoclonal Mouse Anti-
Human Desmin
Dakocytomation, Glostrup,
Denmark, code M0760
Monoclonal Primary
Antibodies
1:50 1 hour
Monoclonal Mouse Anti-
Human Cytokeratin 19
Dakocytomation, Glostrup,
Denmark, code GA615
Monoclonal Primary
Antibodies
1:50 1 hour
One-step polymer-HRP
reagent
Emergo Europe, The Hague,
The Netherlands, code
HK59506K
Anti-mouse and anti-rabbit
secondary antibodies labeled
with enzyme polymer
Ready to use 15 minutes

Intermediate laments in camel kidney
390
RESULTS
General histological overview of the camel
kidney
The kidney was covered by a thick brous capsule
which was composed of inner and outer layers
(Fig. 1A). The inner layer contained numerous
smooth muscle cells, while the outer layer was
predominately composed of dense irregular
connective tissue (Fig. 1A). The kidney parenchyma
was divided into an outer cortex and an inner
medulla (Fig. 1A, B). Cortical and juxtamedullary
nephrons were observed in the kidney. The renal
corpuscles of cortical nephrons were located in
the outer region of the cortex, while the corpuscles
of juxtamedullary nephrons were situated in the
inner cortical region. The loops of Henle in cortical
nephrons were short in contrast to the long loops of
juxtamedullary nephrons, which extended into the
medulla. The cortical region of the kidney contained
renal corpuscles, proximal and distal convoluted
tubules, as well as blood vessels (Fig. 1C, D). The
renal corpuscles were composed of a glomerulus
and glomerular capsule (Bowman’s capsule). The
glomerulus was formed by glomerular capillaries
and mesangial cells (Fig. 1C). The glomerular
capsule was formed by an inner visceral and
an outer parietal layer. The visceral layer was
composed of podocytes, which contained large,
irregular-shaped nuclei, while a simple squamous
epithelium formed the parietal layer (Fig. 1C).
The medulla of the kidney was subdivided into
outer and inner regions, both of which contained
collecting ducts. The outer region of the medulla
Fig. 1.- Photomicrographs of the cortex (A, C, D) and medulla (B) of the camel kidney. H&E staining. (A) Renal capsule and cortex.
OC: Outer region of the renal capsule. IC: Inner region of the renal capsule. Inset: high magnication of inner region of the renal
capsule containing smooth muscle cells (Arrows). (B) Outer region of the medulla. Limbs of the loop of Henle. TA: Thick ascending
limb. TD: Thick descending limb. tLH: Thin limbs. Arrow: Vasa recta. (C) Renal cortex. G: Glomerulus. Arrowhead: Parietal layer
of glomerular capsule. P: Proximal convoluted tubules. Dt: Distal convoluted tubule. CD: Collection ducts. Inset: Renal corpuscle.
Small arrowheads: Podocytes. Small arrow: Intraglomerular mesangial cell. Large arrow: Endothelium of the glomerulus. Large
arrowhead: Parietal layer of glomerular capsule. (D) Renal cortex. G: Glomerulus of a juxtamedullary nephron. Arrowhead: Parietal
layer of a glomerular capsule. TD: Thick descending limb of the loop of Henle. CD: Collecting duct. P: Proximal convoluted tubules.
Arrows: Blood vessels. Scale bars: 50 µm for A, B, C, D.

Lemiaa Eissa et al.
391
additionally contained the thick descending and
ascending, as well as the thin limbs of the loop
of Henle (Fig. 1B). In contrast, the thin limbs of
the loops of Henle were the only tubular nephron
components observed in the inner medulla.
Immunohistochemistry
The immunoreactivity of intermediate laments
in various regions of the camel kidney is shown in
Table 2.
Vimentin
Strong vimentin immunostaining was demon-
strated in podocytes which formed the visceral
layer of the glomerular capsule (Fig. 2 A, B). Im-
munoreactivity was strong to moderate in cells
forming the parietal layer of the glomerular cap-
sule. However, interspersed between the vimen-
tin immunoreactive cells were non-reactive cells
(Fig. 2B). The thin limbs of the loops of Henle in
cortical nephrons displayed strong vimentin im-
munoreactivity (Fig. 2C), whereas those of the
juxtamedullary nephrons were non-reactive to
vimentin (Fig. 2C, D and E).
Endothelial cells of renal blood vessels were
predominantly immunoreactive to vimentin. In
the cortex, these immunoreactive endothelial
cells appeared to be mainly conned to cortical
arteries and glomerular arterioles (Fig. 2A). In the
medulla, strong immunoreactivity for vimentin
was observed in the endothelial cells of the vasa
rectae (Fig. 2C, D and E). However, in the medulla
a few vasa rectae were lined by endothelia that
non-reactive to vimentin (Fig. 2E).
Stromal cells in the interstitial tissue of the
medulla and subepithelial connective tissue of the
renal papilla exhibited strong immunoreactivity
for vimentin (Fig. 2F). In addition, moderate to
weak vimentin immunostaining was observed in
broblasts located in the renal capsule, as well as
in the trabeculae between nephrons.
No vimentin immunoreactivity was observed in
the intraglomerular mesangial cells, epithelium
of proximal and distal tubules (Fig. 2B), and
collecting ducts (Fig. 2E, F).
Smooth muscle actin and desmin
Strong smooth muscle actin immunoreactivity
was detected in intraglomerular mesangial
cells (Fig. 3A, B). Strong smooth muscle actin
immunoreactivity was also noted in the parietal
cells of the glomerular capsules. However, some
of the parietal cells were non-reactive to smooth
muscle actin (Fig. 3B). Intense smooth muscle
actin immunostaining was evident in smooth
muscle cells forming the inner layer of the renal
capsule (Fig. 3C). Additionally, strong smooth
muscle actin immunostaining was demonstrated
in the tunica media and tunica externa of
muscular arteries (Fig. 3A, D), as well as in
pericytes enclosing intertubular capillaries (Fig.
3C, D). In the medulla strong smooth muscle actin
immunoreactivity was observed in the tunica
media of vasa rectae (Fig. 3E, F).
Table 2. The intensity of the immunostaining of vimentin, smooth muscle actin, desmin, and cytokeratin 19 in the kidney of the camel.
Structures Vimentin SMA Desmin Cytokeratin 19
Podocytes +++ - - -
Parietal cells of the glomerular capsule -/++/+++ -/+++ - -
Intraglomerular mesangial cells - +++ + -
Cells of the thin limb of the loop of Henle* +++ - - -
Endothelial cells -/+++ - - -
Vascular smooth muscle cells - +++ + -
Fibroblasts in the renal capsule + - - -
Smooth muscle bres in the renal capsule - +++ - -
Stromal cells below epithelium of renal papilla +++ +++ - -
Stromal cells in connective tissue trabeculae +/++ +++ - -
Fibroblasts in the interstitial tissue of medulla +++ - - -
* The loop of Henle of the outer cortical nephron

Intermediate laments in camel kidney
392
Fig. 2.- Photomicrographs of vimentin immunostaining in the cortex (A and B) and medulla (C, D, E and F) of the camel kidney.
(A) Arrows: Strong vimentin immunopositive podocytes. Black arrowhead: Immunopositive endothelial cell of a small artery.
White arrowhead: Immunopositive endothelial cell of a glomerular arteriole. (B) Black arrow: Strong vimentin immunostaining
in a podocyte. Small white arrowhead: Strong vimentin immunostaining in a cell in the parietal layer of a glomerular capsule.
Black arrowheads: Vimentin immunonegative cells in the parietal layer. Large white arrowhead: Vimentin immunonegative
intraglomerular mesangial cell. Small white arrow: Vimentin immunonegative epithelium of a proximal convoluting tubule. Large
white arrow: Vimentin immunonegative epithelium of a distal convoluting tubule. Inset: High magnication of a glomerulus and
glomerular capsule. Arrow: Vimentin immunopositive podocyte. (C) White arrowheads: Vimentin immunopositive cells forming
the thin limbs of the loop of Henle in supercial nephrons. Arrows: Immunopositive endothelial cells of vasa rectae in the outer
medulla. Black arrowheads: Immunonegative cells of thin limbs of the loops of Henle in juxtamedullary nephrons. Inset: Arrow:
Immunopositive endothelium of a vasa recta. (D) Arrowheads: Vimentin immunonegative cells lining the thin descending limbs
(tD) of loops of Henle in juxtamedullary nephrons. Arrow: Immunopositive endothelium of a vasa recta at the junction between
outer and inner regions of the medulla. TD: Thick descending limb of a loop of Henle. (E) White arrows: Immunopositive endothelial
cells of vasa rectae in the inner medulla. Black arrows: Immunonegative endothelial cells. Black arrowheads: Immunonegative cells
of thin limbs of the loops of Henle of juxtamedullary nephrons. White arrowheads: Immunonegative cells of collecting ducts. (F)
Arrows: Immunopositive stromal cells in the interstitial tissue of the medulla. Black arrowheads: Immunopositive stromal cells in
the subepithelial connective tissue of a renal papilla. White arrowheads: Immunonegative cells of collecting ducts. Scale bars: 100
µm for A, C; 20 µm for B, D, F; 50 µm for E.

Lemiaa Eissa et al.
393
Desmin immunostaining was restricted to
intraglomerular mesangial and vascular smooth
muscle cells (Fig. 4A, B). The proximal and distal
convoluted tubules, as well as the collecting ducts
were reactive to vimentin, smooth muscle actin,
desmin, and cytokeratin 19.
Fig. 3.- Photomicrographs of smooth muscle actin immunostaining in the cortex (A and B) and medulla (C, D, E and F) of the camel
kidney. (A) Smooth muscle actin immunoexpression in intraglomerular mesangial cells (arrows), as well as in the tunica media
(TM) of a muscular artery (MA) and glomerular arteriole (GA). Smooth muscle actin immunoexpression is also present in smooth
muscle cells in the tunica externa (arrowhead) of the muscular artery. (B) Smooth muscle actin immunostaining in the cytoplasm
of intraglomerular mesangial cells (arrows), as well as in the parietal cell layer (arrowhead) of the glomerular capsule. Inset:
Arrow: Vimentin immunonegative cell in the parietal layer of a glomerular capsule. (C) Smooth muscle actin immunoreactivity in
smooth muscle cells of the renal capsule (arrows), as well as in a pericyte of a capillary (arrowhead) interposed between a proximal
convoluted tubule (PCT) and a cortical collecting duct (CD). (D) Strong smooth actin immunostaining in the tunica media (TM) of
a muscular artery, as well as in a pericyte of an intertubular capillary (arrowhead). Arrow: Smooth muscle actin immunonegative
endothelium. (E) & (F) Arrows: Strong smooth muscle actin immunoreactivity in smooth muscle cells of the tunica media of the
vasa rectae. RT: Renal tubules. Scale bars: 20 µm for A, B, C, D, F; 100 µm for E.

Intermediate laments in camel kidney
394
Cytokeratin 19
No immunoreactivity for cytokeratin 19 was
detected in the camel kidney.
DISCUSSION
Renal capsule
The renal capsule is known to play a role
in the establishment of an effective renal
interstitial pressure (Khraibi and Knox, 1989),
and subsequently water excretion (Farrugia et
al.,1992). The presence of smooth muscle cells
in the inner capsular layer of camel kidney has
previously been reported by Eissa et al. (2018),
and conrmed in the current study. The present
study has shown that the smooth muscle cells
are immunoreactive for smooth muscle actin,
but non-reactive to desmin. The occurrence of
smooth muscle cells in the renal capsule has
been reported in several mammalian species and
is known to be involved in the contractile ability
of the capsule (Kobayashi, 1978). In addition,
the thick collagenous layer of the renal capsule
functions to protect the kidney from traumatic
injuries (Orchard et al., 2014). Thus, as shown
in the current study, the main component of the
outer region of the renal capsule dense irregular
connective tissue with associated vimentin
immunoreactive broblasts. Fibroblasts have
been considered as one of the major components
of renal capsule in several mammals, such as
mouse, rat, guinea pig and rabbit (Kobayashi,
1978). In addition, broblast in the kidney were
demonstrated by the immunolocalization of
vimentin (Boor and Floege, 2012).
Renal parenchyma
The general histomorphological ndings of the
present study were similar to those reported in
Fig. 4.- Photomicrograph of desmin immunostaining in the cortex of camel kidney. Immunopositive intraglomerular mesangial
cells (arrowheads). Immunopositive smooth muscle cells of a glomerular arteriole (arrows). Scale bar: 30 µm.

Lemiaa Eissa et al.
395
previous investigations on the camel (Abdalla and
Abdalla, 1979; Beniwal et al., 1998; Wenhui and
Huaitao, 2000; Xu et al., 2009). Furthermore, the
present study conrmed that the renal histology of
the camel does not differ signicantly from other
mammalian species, such as the dog (Bulger et al.,
1979), cattle (Mbassa, 1988), and sheep (Singh et
al., 2018).
In this study, vimentin was immunolocalized
in podocytes, vascular endothelial cells, and
medullary interstitial broblasts. These ndings
are plausible as it is known that vimentin occurs
in cells of mesenchymal origin (Leong et al., 2003;
Satelli and Li, 2011). In addition, these results
are in agreement with studies carried out on
several mammals, including the human (Essawy
et al., 1997), domestic ruminants (Maretta and
Marettová, 1999; Yaoita et al., 1999), rodents (Zou
et al., 2006; Yaoita et al., 1999; Sistani et al., 2013)
dog (Yaoita et al., 1999), and polar fox (Laszczyńska
et al., 2012). Intraglomerular mesangial cells,
and the epithelia of proximal and distal tubules
in the current study did not react with vimentin.
These reports are contrary to observations
made in the human and polar fox in which
vimentin immunoreactivity was demonstrated
in the epithelia of the proximal and distal tubules
(Laszczyńska et al., 2012; Smeets et al., 2013).
Furthermore, intraglomerular mesangial cells in
humans, rats, ruminants, and polar foxes have
been reported to be immunoreactive for vimentin
(Stamenkovic et al., 1986; Oosterwijk et al.,
1990; Scanziani et al., 1993; Essawy et al., 1997;
Maretta and Marettová, 1999; Yaoita et al., 1999;
Zou et al., 2006; Laszczyńska et al., 2012; Smeets
et al., 2013). These results indicate that species
variations exist in the immunolocalization of
vimentin in the mammalian kidney. However,
the functional signicance of these interspecies
variations is unknown.
In the current study smooth muscle actin
immunoreactivity was detected in the tunica
media of blood vessels throughout the renal
tissue. This is similar to ndings reported in the
rat (Carey et al., 1992) and human (Essawy et al.,
1997; Novakovic et al., 2012). Smooth muscle actin
has also been demonstrated in myobroblasts
located in the interstitium of normal human
kidney (Essawy et al., 1997; Gonlusen et al., 2001).
In the present study no myobroblasts appeared
to be present.
The current ndings revealed that smooth
muscle actin immunostaining was demonstrated
in the parietal layer of the glomerular capsule.
This may suggest a contractile function of the
parietal cells of camel kidney. Interestingly, the
present study showed that some of the parietal
cells of the glomerular capsule were non-reactive
when stained either with vimentin or smooth
muscle actin. It is plausible that the negative
parietal cells for vimentin might display positive
reactivity for smooth muscle actin, and the reverse
is true. However, further double immunostaining
studies will need to be conducted to conrm this
assertion.
In this study, positive immunostaining for smooth
muscle actin was observed in intraglomerular
mesangial cells. This is in agreement with the
ndings of studies conducted on the human
kidney (Schlӧndorff and Banas, 2009; Young et al.,
2014). It is known that intraglomerular mesangial
cells contain the intermediate laments actin and
myosin (Davies, 1994; Stockand and Sansom,
1998). Consequently, intraglomerular mesangial
cells are thought to have a contractile ability,
which is utilized in the control of glomerular
blood ow (Reece, 2015).
It is noteworthy that the immunostaining of
desmin in this study was weaker than that of
smooth muscle actin. One possible explanation for
this difference could be that the xation of renal
tissue with formalin may signicantly enhance
the immunostaining sensitivity to smooth muscle
actin rather than desmin (Rangdaeng and Truong,
1991). Desmin immunostaining in the present
study was observed primarily in intraglomerular
mesangial cells, as well as in vascular smooth
muscle cells. Similar ndings were reported in
the human (Oosterwijk et al., 1990), rat (Zou et
al., 2006) and polar fox (Laszczyńska et al., 2012).
However, studies by Essawy et al. (1997), as well
as Gonlusen et al. (2001) did not detect desmin
immunoreactivity in the human kidney.
It is known that there are approximately twenty
different types of cytokeratins, with at least two

Intermediate laments in camel kidney
396
occurring in most epithelial cells (Leong et al.,
2003). In the human kidney, cytokeratin 19 has
been demonstrated in the parietal layer of the
glomerular capsule (Stamenkovic et al., 1986), as
well as in the loop of Henle (Achtstätter et al., 1985),
distal convoluted tubules (Oosterwijk et al., 1990)
and collecting ducts (Şen et al., 2010). However, the
current study did not detect cytokeratin 19 in the
camel kidney. It has been reported that laments
generated from different types of cytokeratins
have distinct physical properties, suggesting
tailor-made networks of intermediate laments
suitable for tissue structural requirements of
tensile strength, exibility, and dynamics (Fuchs
et al., 1994). Therefore, it is most likely that the
epithelial cells of the camel kidney may have types
of cytokeratins other than cytokeratin 19.
In conclusion, the results of the present study
have shown that similarities and differences
exist in the immunolocalization of cytoskeletal
proteins in the camel when compared to other
mammals. The presence of smooth muscle actin
immunoreactivity in the parietal cell layer of
the glomerular capsule suggests a contractile
function of the parietal cells in the camel kidney.
Signicantly, the results of the study suggest that
vimentin and smooth muscle actin can be used as
markers for the identication of podocytes and
intraglomerular mesangial cells, respectively, in
the camel kidney.
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