HIV binding, penetration, and primary infection
in human cervicovaginal tissue
Diane Maher*, Xiaoyun Wu†, Timothy Schacker‡, Julie Horbul*, and Peter Southern*§
Departments of *Microbiology and‡Medicine, University of Minnesota Medical School, MMC 196, 420 Delaware Street Southeast, Minneapolis, MN 55455;
and†Department of Medicine, University of Alabama at Birmingham, 1530 Third Avenue South, Birmingham, AL 35294
Edited by Robert C. Gallo, University of Maryland Biotechnology Institute, Baltimore, MD, and approved June 21, 2005 (received for review
February 1, 2005)
We have developed human cervicovaginal organ culture systems
to examine the initiating events in HIV transmission after exposure
to various sources of HIV infectivity, including semen. Newly
infected cells were detected in the cervical submucosa 3–4 days
after exposure to a primary HIV isolate. At earlier times, extensive
and stable binding occurred when cervical surfaces were exposed
to virions or seminal cells. Cervical mucus provided some protec-
seminal cells. Confocal microscopy combined with 3D surface
surface of the cervical epithelium and actually penetrate beneath
the epithelial surface. In quantitative assays, pretreatment with a
blocking antibody directed against ?1 integrin reduced HIV virion
binding. Collectively, these results highlight a continuum of com-
plex interactions that occurs when natural sources of HIV infectiv-
ity are deposited onto mucosal surfaces in the female reproductive
confocal microscopy ? female reproductive tissue ? HIV transmission ?
organ culture ? tissue surface reconstruction
HIV through heterosexual exposure (1–6). There is, however,
only limited information available concerning the specific cel-
lular and molecular events that lead to HIV transmission
through sexual activity. Semen contains either cell-free virus or
cell-associated virus (7–12), and each source of HIV infectivity
may require different mechanisms to establish infection. Clear
understanding of the molecular interactions between sources of
infectivity and mucosal surfaces will be crucial in developing
topical agents to prevent sexual HIV transmission.
The current view of sexual HIV transmission has largely been
developed from simian immunodeficiency virus (SIV) infections
of female nonhuman primates (reviewed in ref. 4). When
macaques were exposed to cell-free SIV intravaginally, infected
resident cells were consistently detected in reproductive tract
tissues before being detected in the draining lymph nodes (13).
Taken together, the data from macaque infections indicate that
SIV (100% infectious dose of cell-free virus) readily traverses an
epithelial surface and establishes focal infections within suscep-
tible resident cells in female reproductive tissues and then the
infection spreads systemically. For heterosexual HIV transmis-
sion, the properties of the infectious inoculum are highly variable
as cell-free HIV virions (12) or HIV-infected cells may be shed
in semen (9). Furthermore, both soluble and cellular constitu-
ents of semen may induce transient changes in exposed epithelial
surfaces, resulting in increased susceptibility to primary HIV
infection (14, 15).
The complex nature of mucosal surfaces presents a major
challenge for comprehensive cellular and molecular studies of
microbial infections (16). The development of organ cultures
with human mucosal tissues has provided some insight into HIV
infection at these sites. Although methods for organ culture have
varied, previous studies with human cervical tissue have shown
oday women account for more than half of the newly
HIV-infected adults worldwide, and most women acquire
that cells in the submucosa are susceptible to HIV infection
(17–19). Additionally, ex vivo organ cultures have been used to
evaluate inhibitors of HIV infection and replication (19–21). We
have previously described binding of HIV virions and seminal
cells to the mucosal surface of palatine tonsil in a reconstruction
of HIV transmission after oral exposure (22). Here, we set out
to study sexual transmission of HIV at mucosal surfaces of the
cervix. The selection of human cervical tissue allowed the study
of both the stratified epithelium of the ectocervix, which closely
resembles the vaginal epithelial surface, and the columnar
epithelium of the endocervix. Each epithelial surface may in-
teract differently with sources of HIV infectivity. Our organ
culture methods have the advantage of using human materials
for the target mucosal tissue and biologically relevant sources of
infectivity: semen from HIV-seropositive donors and a cell-free
stock of HIV virions obtained by limited passage in vitro of a
primary patient isolate.
conditions not involving the cervix were processed in the labo-
ratory within 1–3 h of completion of surgery. The experimental
protocols had full Institutional Review Board approval. Cervical
tissue with external epithelial surfaces (10–25 mm2) was
mounted in agarose medium such that the intact epithelial
surface remained exposed and all cut surfaces were covered with
agarose (22). The stratified epithelium of the ectocervix re-
mained largely intact for up to 48 h, then squamous epithelial
cells sloughed away but the basal epithelial cell layer remained
was retained for 4–6 days and continued to secrete mucus.
(22, 23). Alternatively, in some infections, cervical tissue was
submerged in cell-free virus and then the tissue was cultured on
collagen sponges at the gas-medium interface. In all experiments
reported here, infections were performed with a dual tropic pri-
mary patient isolate (HIV 96-480; refs. 22 and 23), and binding
studies were performed with a noninfectious X4 tropic virion
preparation, HIV-GFP (ref. 22; see Supporting Methods, which is
published as supporting information on the PNAS web site).
Single-cell immunohistochemistry was performed as reported (24).
Blocking Assays, Image Collection, and Quantitative Analysis. Popu-
lations of primary human cervical epithelial cells or 3-mm biopsy
punches of intact human ectocervical epithelium were incubated
with antibodies directed against ?1 integrin, galactose ceramide,
or a mouse IgG control. Antibody treatment began 1–2 h before
the addition of HIV-GFP virions (2.5 ? 108virions) in seminal
plasma (final concentration: 50% seminal plasma, 50% original
This paper was submitted directly (Track II) to the PNAS office.
Abbreviation: SIV, simian immunodeficiency virus.
§To whom correspondence should be addressed. E-mail: email@example.com.
© 2005 by The National Academy of Sciences of the USA
August 9, 2005 ?
vol. 102 ?
blocking solution). After 3 h, samples were washed extensively,
fixed, and quantified for virion binding.
3D Analysis. Tissue surface representations were created with
AMIRA (Mercury Computer Systems?TGS Unit, San Diego) at
the Supercomputing Institute, University of Minnesota.
For further details, see Supporting Methods.
HIV Infection of Cervical Leukocytes. When cell-free HIV (HIV
96-480; a low-passage patient isolate) was applied directly onto
intact epithelial surfaces of embedded cervical tissue, infected
tissue leukocytes were identified at 4–6 days postinfection by
immunocytochemical staining for HIV p24. The infected cells
were situated in the submucosa, in immediate proximity to the
exposed endocervical epithelium (representative experiment
shown in Fig. 1 A-C, day 4 postinfection). Under these culture
conditions, the endocervical columnar epithelium remained
intact and the epithelial cells secreted large amounts of mucus
(Fig. 1 D and E). In an alternative infection strategy, designed to
simulate HIV exposure at a damaged epithelium, cervical tissue
was submerged in cell-free virus for 4 h followed by culture on
collagen sponges. Leukocytes expressing p24 were detected in
the submucosa at 3–9 days postinfection (Fig. 1 F and G, day 3
postinfection). Other HIV infection studies have included cyto-
kine activation of target cell populations (19, 21), but the
infections with HIV 96-480 were established without exogenous
cell stimulation. However, in two of eight tissues exposed to HIV
infectivity we did not detect any infected target cells and this
outcome may have been changed by ex vivo cellular activation
signals. Collectively, the results shown in Fig. 1 validate the
infection of cervical organ cultures with a primary isolate of HIV
and provide specific information from a human experimental
system that matches the early time point analysis of SIV vaginal
infection in rhesus macaques. In both situations, infected leu-
kocytes were detected at low frequency in proximity to exposed
Cells from Semen Bind and Penetrate Mucosal Surfaces but Also
during the 3- to 4-day incubation period required to detect newly
infected cells, we recognized that significant changes were
occurring at the exposed epithelial surfaces. Cell sloughing and
degeneration of stratified epithelium during the extended incu-
bation obscured the earliest physical interactions supporting the
initiation of HIV infection in ectocervix organ cultures. There-
fore, we developed procedures to characterize events occurring
within the first 24 h after exposure to HIV. Tissue pieces were
embedded in agarose and exposed to sources of HIV infectivity
(seminal cells or cell-free virions) and then large areas of
undisturbed epithelial surface were surveyed by confocal mi-
croscopy with a water immersion lens. Viable seminal cells
surface of the cervix. seminal cells were prelabeled with 5-(and 6)-
carboxyfluorescein diacetate succinimidyl ester (CFSE) (green), and the epi-
thelium was stained with either Cell Tracker orange (red, A, D, and E) or
ethidium homodimer-II (red, B and C). Images are representative of binding
of 81 images collected at 1-?m steps in the z axis. (B) Seminal cells remain
suspended in mucus secreted by the columnar epithelial cells of the endocer-
vix: 18-h exposure. Brightest point projection of 15 images collected at 3-?m
steps in the z axis. (C) Seminal cells penetrate the mucus and reach the
columnar epithelial surface. The same field as shown in B, focusing on the
endocervical tissue surface. Brightest point projection of 19 images collected
at 3-?m steps in the z axis. (D and E) Penetration of the stratified epithelium
by seminal cells. Each image shows an 8-?m cross section cut from the tissue
shown in A (counterstained with DAPI, blue). (Scale bars: 20 ?m.)
Interactions between viable seminal cells and the intact mucosal
cervical leukocytes by cell-free HIV. (A–C, F, and G) Immunohistochemical
detection of HIV p24 gag (brown signal) 4 days (A–C) or 3 days (F and G)
postinfection. Images are representative of experimental infections with
cervical tissue from six independent tissue donors. (A) Transfer of infectivity
through an intact endocervical epithelium: a p24-positive intraepithelial leu-
kocyte directly beneath the columnar epithelium. (B) High magnification of
the boxed area shown in A. (C) High-power image showing an additional
p24-positive cell in close proximity to the epithelium. (D and E) Retention of
columnar epithelium in organ culture. Representative image showing the
integrity of columnar epithelium and continued secretion of mucus (arrow)
after 4 days of culture (hematoxylin?eosin, same tissue as shown in A–C). (F)
HIV infection of cervical tissue by submersion: numerous p24-positive cells
within the submucosa of endocervical tissue. (G) High magnification of the
boxed area shown in D. (Scale bars: A, E, and F, 50 ?m; B, C, and G, 20 ?m; D,
Reconstruction of sexual HIV transmission: de novo infection of
Maher et al.PNAS ?
August 9, 2005 ?
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[labeled with 5-(and 6)-carboxyfluorescein diacetate succinimi-
extensively to the stratified epithelium of the ectocervix (Fig.
2A). For the endocervix, the vast majority of seminal cells
remained suspended in mucus secreted by the columnar epithe-
lial cells (Fig. 2B) but some cells did penetrate through the
mucus to contact the epithelial cell surface (Fig. 2C). Systematic
analysis of cross sections, cut in an orientation-specific manner,
revealed that both spermatozoa and seminal round cells (see
Supporting Methods) had penetrated beneath the most external
layer of ectocervical epithelial cells (Fig. 2 D and E). In cross
sections from the exposed endocervical tissues, many seminal
cells were detected in close proximity to the epithelial cell
surface and within glandular folds of the endocervix, still
suspended in mucus (data not shown). The observed distribution
of seminal cells at exposed tissue surfaces is biologically relevant
to HIV transmission because HIV virions have been reported to
attach to the midportion of spermatozoa (25), and HIV-infected
leukocytes can be shed in semen (9). Binding and invasion by
male cells could deliver HIV infectivity directly to target cells in
female cervicovaginal tissue, and?or male cells may induce
transient perturbations in epithelial integrity, resulting in ele-
vated susceptibility to HIV infection (15).
HIV Virions Remain Trapped in Cervical Mucus. In a series of related
binding experiments, we exposed endocervical epithelium to a
reconstituted inoculum: seminal plasma plus fluorescent HIV
virions (HIV-GFP; a noninfectious preparation of HIV that
incorporates GFP into virions, see Supporting Methods). The
majority of virions remained suspended in mucus but limited
numbers of virions were detected in cross sections at or beneath
the endocervical epithelial surface (Fig. 3 A and B). Because
each cross section contains only information from a tiny area of
epithelium, we recognized that a broader perspective could be
gained by analyzing confocal information from intact, undis-
turbed tissue surfaces. Confocal images are frequently displayed
as brightest point projections (Fig. 3C) but this format does not
the 3D visualization and volume modeling software program
AMIRA, we created images that display the 3D structure of an
epithelial surface and the spatial locations of HIV virions (Fig.
3D). When the 3D image was rotated (compare Fig. 3 E with F,
also see Movie 1, which is published as supporting information
on the PNAS web site), it became clear that most of the virions
were suspended in mucus above the columnar epithelial cells.
These findings provide evidence that the amount and composi-
tion of cervical mucus may influence sexual routes of HIV
transmission (26, 27).
HIV Virions Bind and Penetrate the Stratified Epithelium. When the
stratified epithelium of ectocervix was exposed to HIV-GFP
virions in seminal plasma, confocal images revealed stable virion
binding to the epithelial cell surface and penetration of some
virions beneath the epithelial cell surface (Fig. 4). The precise
location of virions, with respect to the ectocervical surface, was
established from 3D representations combined with adjustments
to the transparency of the surface cells (Fig. 4 C and D, AMIRA).
Rapid penetration of HIV virions beneath the ectocervical
visualization of virions trapped in cervical mucus. (A and B) HIV-GFP virions,
green. Nuclei, blue, DAPI. (C–F) HIV-GFP virons, green. Epithelium, red, Cell
in cervical mucus. In this experiment HIV-GFP virions were incubated with
endocervical tissue for 2 h in the presence of seminal plasma. After washing,
the tissue was cultured for an additional 24 h and then washed and fixed.
Arrows indicate representative virions that have penetrated beneath the
epithelial surface. (B) An 8-?m cross section from the same donor shown in A,
but not exposed to HIV-GFP. (C) HIV virions remain in the mucus after a 2-h
exposure as shown by the green signal on the lower left. This image shows a
brightest point projection of 120 images collected at 1-?m steps in the z axis.
as a 3D reconstruction of endocervical topology. (E and F) Magnified views of
the image shown in D. F has been rotated to show that the virions are not
attached to the columnar epithelial cells. The circled area identifies the same
to the surface. See Movie 1. (Scale bars: A and B, 20 ?m; C, 25 ?m; D, 200 ?m;
E and F, 100 ?m.)
Surface reconstruction of endocervical columnar epithelium and
ization of bound and internalized virions. HIV-GFP virions, green; epithelium,
red. (A–D) Ethidium homodimer II. (E) Cell Tracker orange. Images are repre-
sentative of binding experiments with 13 independent tissue donors. (A) HIV
virions bound to stratified epithelial cells: 2-h exposure in seminal plasma.
Shown is a brightest point projection of 66 images collected at 1-?m steps in
displayed as a 3D topographical reconstruction. (C) An enlarged and rotated
epithelial cell. (D) The same image as in C, with the cellular surface rendered
semitransparent to reveal virions located beneath the external surface. (E) An
8-?m cross section from an independent experiment showing virions located
beneath the external surface after a 2-h incubation with HIV-GFP virions
suspended in seminal plasma. (Scale bars: A–D, 50 ?m; E, 20 ?m.)
Reconstruction of the stratified ectocervical epithelium and visual-
www.pnas.org?cgi?doi?10.1073?pnas.0500848102Maher et al.
epithelial cell surface was confirmed by conventional cross-
sectional analysis in independent experiments (Fig. 4E). The
finding that HIV virions in seminal plasma readily penetrate into
the epithelium of the ectocervix is particularly significant be-
cause a similar type of stratified epithelium lines the entire
vaginal cavity. Additional experiments, with tissue from a dif-
ferent donor, focused on virion binding in the cervical junction
region, corresponding to the transition from stratified epithe-
lium of the ectocervix to columnar epithelium of the endocervix.
In this location there was minimal mucus secretion, and both
were readily observed in the presence of seminal plasma (Fig. 5).
Inhibition Assays Indicate a Role for ?1 Integrin in Virion Binding to
Cervical Epithelium. As a step toward defining the specific inter-
actions supporting virion binding at epithelial surfaces, we
developed quantitative assays for HIV virion binding to epithe-
lial cells, in the presence of seminal plasma. Because CD4 is
generally not expressed on epithelial cells, the fundamental
interaction between cell surface CD4 and HIV gp120 cannot
account for virion binding to epithelial cells (28). However, in
virions by binding to gp120 (29, 30). Fibronectin-coated virions
could then bind to ?1 integrin expressed on epithelial surfaces.
For initial binding experiments, we used primary human epi-
thelial cells, grown from cervical tissue explants, that expressed
cytokeratins and consistently formed tight junctions (data not
shown for cervix; see refs. 22 and 23 for a description of primary
tonsil epithelial cells). HIV-GFP virions readily bound to pri-
mary cervical epithelial cells in the presence of seminal plasma
(Fig. 6A, 3-h exposure). Pretreatment of primary cervical cells
with an antibody that blocked the interaction of ?1 integrin with
fibronectin reduced the number of bound virions relative to
paired samples exposed to a control antibody (Fig. 6D). We also
an alternative HIV receptor that is present on some epithelial
cervical epithelial cell populations (Fig. 6D). The variability in
blocking may be explained by differences in the expression levels
for galactose ceramide at the cell surface in independent pop-
ulations of primary cervical epithelial cells.
Binding inhibition assays were also performed with intact
tissue pieces, using 3-mm punch biopsies collected in adjacent
sequence from a large contiguous area of ectocervix (Fig. 6B).
in these experiments bound to the external cells of the stratified
ectocervical epithelium (Fig. 6C and data not shown). Substan-
tial inhibition of HIV-GFP virion binding was observed with two
two of four donors tested with anti-galactose ceramide antibody
(Fig. 6E). Immunocytochemical detection of ?1 integrin expres-
sion on stratified squamous epithelium from 10 randomly se-
lected cervix tissue samples (tissues fixed immediately on receipt
in the laboratory) revealed variable levels of expression between
tissue donors (data not shown). The variation of ?1 integrin
expression may explain the broad range of inhibitory effects
observed in the quantitative binding assays but, in situations
where extensive inhibition of HIV-GFP virion binding did occur,
our results strongly suggest that a major component of HIV
binding to epithelial surfaces involves recognition of ?1 integrin.
We have developed organ culture systems to reconstruct key
elements of HIV sexual transmission, by combining viable
human cervicovaginal tissue, HIV virions, and the cellular and
soluble constituents of human semen. Other studies that used
human organ culture techniques to document physical transfer
of HIV virions across epithelial surfaces drew criticism be-
cause of uncertainties regarding virion leakage around the
tissue pieces (18, 32, 33). With these concerns in mind, we
focused exclusively on the detection of individual HIV-
infected cells and direct visualization of bound virions and cells
at and beneath the exposed mucosal surfaces. A primary
patient isolate of HIV established infection in resident endo-
cervical leukocytes, at low frequency, when the virus was
applied to an intact epithelial surface. This mode of HIV
germ agglutinin (Alexa Fluor-633 conjugate) to identify cell borders, Golgi, and endoplasmic reticulum; nuclei remain unstained. (A) HIV-GFP virions bound to
the junction region of the cervix, after 3 h of exposure to virions in the presence of seminal plasma; brightest point projection of 92 images collected at 1-?m
(indicated by circles) that have penetrated beneath the tissue surface. (Scale bars: A and B, 50 ?m; C and D, 10 ?m.)
Maher et al. PNAS ?
August 9, 2005 ?
vol. 102 ?
no. 32 ?
infection deliberately excluded external activation of target
cervical tissues to make the experimental systems conform as
closely as possible to the biological reality of HIV transmis-
sion. However, preexisting inflammation in the female repro-
ductive tract can increase susceptibility to HIV infection (5, 27,
34). The tissue distribution of susceptible CD4-positive T cells,
together with morphological abnormalities in different muco-
sal surfaces, may contribute to the variability associated with
community HIV transmission.
Studies using immortalized epithelial cells or primary pop-
ulations of epithelial cells have suggested that epithelial cells
are able to sequester HIV virions and that the heparan sulfate
moieties of cell surface proteoglycans are involved in virion
attachment to an ectocervical cell line (35, 36). We developed
quantitative assays to study virion binding to both primary
cervical epithelial cell populations and intact cervical epithe-
lium, and we routinely included seminal plasma. Semen con-
tains high levels of fibronectin, which has been shown to bind
to viral gp120 (29, 30) and ?1 integrin is a ubiquitous molecule
involved in fibronectin binding. We therefore speculated that
fibronectin may facilitate virion binding to mucosal surfaces by
forming a link between HIV gp120 and ?1 integrin. The
addition of a blocking antibody to ?1 integrin effectively
decreased virion binding to primary epithelial cells. Subse-
quent experiments to block virion binding to intact cervical
epithelium produced more variable results, presumably re-
flecting variability in ?1 integrin surface expression levels
across a tissue piece and additional variability between tissue
donors. One element of donor-to-donor variability may be
attributed to hormonal effects on the epithelial surfaces,
according to the stage of the menstrual cycle (37). The
apparent discrepancies between virion binding to primary cells
and tissue pieces emphasize the importance of maintaining the
closest possible link between the assay and the biological
process under consideration. As virion binding to either
primary cells or intact cervical mucosa was not inhibited
completely by the blocking antibodies tested, other cell surface
molecules may be involved in virion–epithelial cell binding.
Additionally, in related experiments we observed that inert
latex spheres (0.1 ?m diameter) can bind or become trapped
on mucosal surfaces (data not shown). If nonspecific mecha-
nisms can also cause retention of virions, then nonspecific
events may account for part of the binding not blocked by
treatment with specific antibodies. In developing a compre-
hensive understanding of primary HIV transmission, it is
important to recognize that a spectrum of both specific and
nonspecific interactions may contribute to retention of HIV
infectivity at mucosal surfaces until the first cycle of productive
In cervicovaginal organ cultures that have been designed to
simulate sexual HIV transmission, we have observed rapid and
extensive binding of HIV virions and penetration beneath the
most external epithelial cell layers. For HIV transmission to
occur in a community exposure, progression to the next event
may require a chance encounter with a susceptible cell [CD4-
positive T cell or macrophage or uptake by a dendritic cell (38,
39)] or the exposure may not result in primary infection. Virion
binding without transmission may occur frequently, as epidemi-
ological studies suggests that 1 in 200–1,000 exposures leads to
HIV infection (1, 40). Immunohistochemical staining of 10
randomly selected cervical tissues (10 different tissue donors;
tissue fixed immediately on receipt in the laboratory) with
antibodies directed against CD3, CD4, and CD45RO [clone
UCHL-1 (41)] revealed a broad distribution of activated T cells,
ranging from occasional positive cells to focal accumulations of
activated T cells. Overall, the submucosa of the endocervix
consistently contained more CD4-positive cells than the ecto-
cervix (data not shown). The differences observed in T cell
numbers and distribution between different tissue donors may
relate to the variability of HIV transmission rates in community
Our results with human tissue and HIV are consistent with
findings from vaginal SIV infections in macaques because HIV
exposure in the organ culture systems also leads to initial
infection of only small numbers of resident leukocytes in cervi-
covaginal tissues. However, as a consequence of extensive virus
amplification and rapid systemic dissemination, observed in both
macaques and patients with acute retroviral syndrome, any
realistic strategy to curtail HIV transmission must include
protection of resident tissue leukocytes that could become
infected after HIV exposure (4). Given the extent of virion and
cell binding to mucosal epithelial surfaces, any mechanism to
reduce binding could diminish HIV transmission.
We thank our Department of Microbiology colleagues, Dr. Ashley
Haase, Dr. Kathryn Staskus, Dr. Pamela Skinner, Dr. Jake Estes, and
Stephen Wietgrefe, and Dr. Stefan Pambuccian in the Department of
Surgical Pathology, University of Minnesota Medical School, for invalu-
able advice and insightful critiques; and Drs. Wade Bresnahan, Paul
Bohjanen, and Hae-Sun Park for thoughtful reviews of the manuscript.
This work would not have been possible without the skillful assistance of
Ms. Diane Rauch and Ms. Sarah Bowell in the Tissue Procurement
titative binding and blocking assays. (A and B) Representative brightest-point
projections used for quantitative image analysis showing HIV-GFP virions
(B). Cells and tissue counterstained with wheat germ agglutinin (Alexa Fluor-
633 conjugate) are shown in red. (C) Representative image showing the
blocking antibody to ?-1 integrin (brown) binding to the external cells of the
ectocervical epithelium. (D and E) Quantitative image analysis of HIV virion
binding in the presence of seminal plasma to primary epithelial cells (D, four
independent experiments with different primary cell populations from four
five independent experiments with tissue from five different cervical tissue
samples, Cx5–Cx9). Data shown have been normalized to the isotype control
antibody (mIgG) and represent particle counts from 10 fields for each exper-
imental condition. Error bars indicate the SEM.*, P ? 0.05, Student’s t test
against the control sample. ND, not done. (Scale bars: A–C, 20 ?m.)
Interactions between HIV virions and cervical epithelial cells: quan-
www.pnas.org?cgi?doi?10.1073?pnas.0500848102Maher et al.
Facility,FairviewUniversityMedicalCenter,Minneapolis,andMatthew Download full-text
Larson in the Department of Medicine, University of Minnesota, who
were collectively responsible for the primary interactions with the
patients. We greatly appreciate the willingness of many anonymous
donors to provide samples for research purposes and the essential
contributions provided by the staff and resources within the Bioimaging
and Processing Laboratory and the Supercomputing Institute at the
University of Minnesota. This work was supported by National Institutes
of Health Grants DE 15090 (to D.M., J.H., and P.S.) and DK 64400 and
AI 49806 (to X.W.).
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