Independence of Granzyme B Secretion and Interferon‐γ Production during Acute Simian Immunodeficiency Virus Infection

William Penn University, Filadelfia, Pennsylvania, United States
The Journal of Infectious Diseases (Impact Factor: 6). 06/2006; 193(10):1441-50. DOI: 10.1086/503364
Source: PubMed


Quantification of interferon (IFN)-gamma by enzyme-linked immunospot (ELISPOT) assay is currently used as a surrogate measurement of cytotoxic T lymphocyte (CTL) activity in nonhuman primates, particularly in simian immunodeficiency virus (SIV) models. Given that noncytotoxic cells and natural killer cells can also release IFN-gamma, quantification of granzyme B (GrB), a molecule secreted predominantly by activated CD8+ T cells, may represent an additional surrogate measurement of CTL activity.
We evaluated, by ELISPOT assay, GrB activity in response to 3 overlapping SIV Gag peptide pools in 18 rhesus macaques with acute SIVmac251 infection and analyzed its correlation with IFN-gamma ELISPOT responses and plasma viral load.
SIV Gag-specific GrB activity increased from 3.9- to 14.4-fold after infection, compared with that observed before infection. GrB secretion did not correlate directly with IFN-gamma production. Importantly, SIV Gag-specific IFN- gamma production was negatively correlated with plasma viral load, whereas GrB activity was not. However, the peak of GrB activity coincided with the lowest plasma viral load detected after infection, whereas the magnitude of IFN-gamma production was 1.8-fold lower than the GrB response; these results illustrate that the responses differ.
Our data support the concept that the GrB and IFN-gamma ELISPOT assays measure immune responses in different immune-cell populations with unique specificities.

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    • "The breadth of the response differed between each animal with only the immunodominant Gag_CM9 (Allen et al., 1998) detected in all 5 macaques. CD8 + T cells that have cytolytic effector function may be critical for control of HIV/SIV replication (Calarota et al., 2006; Goulder et al., 2000; Yang et al., 1997), but IFN-γ-producing CD8 + T cell responses detected by the ELISPOT assay do not always correlate with the cytolytic effector response (Calarota et al., 2006). To determine if the HBcAg-multi-epitope DNA vaccine induced CD8 + T cells with cytolytic activity, a second group of macaques was immunized with 3 doses of HBc-multiepitope DNA vaccine without the plasmid expressing whole tat, and cytolytic effector responses were assayed by 51 Cr-release assay. "
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