Prevention of immunodeficiency virus induced CD4+ T-cell depletion by prior infection with a non-pathogenic virus

Abstract

Immune dysregulation initiated by a profound loss of CD4+ T-cells is fundamental to HIV-induced pathogenesis. Infection of domestic cats with a non-pathogenic lentivirus prevalent in the puma (puma lentivirus, PLV or FIV(pco)) prevented peripheral blood CD4+ T-cell depletion caused by subsequent virulent FIV infection. Maintenance of this critical population was not associated with a significant decrease in FIV viremia, lending support to the hypothesis that direct viral cytopathic effect is not the primary cause of immunodeficiency. Although this approach was analogous to immunization with a modified live vaccine, correlates of immunity such as a serum-neutralizing antibody or virus-specific T-cell proliferative response were not found in protected animals. Differences in cytokine transcription profile, most notably in interferon gamma, were observed between the protected and unprotected groups. These data provide support for the importance of non-adaptive enhancement of the immune response in the prevention of CD4+ T-cell loss.

Figure 1

Mean PLV viral copy number per 1 million PBMCs as measured by real-time PCR in groups inoculated with PLV or medium only on day 0. Bars indicate the standard deviation. Arrow indicates the inoculation of 5 animals with FIV (striped bars). N = 10 for days 3, 10, 17 and 24 and n = 5 for day 31 and thereafter. A number less than 5 above the standard deviation bar indicates the number of animals that had copy numbers above the lower limit of detection. Calculation of means used values for only those animals with detectable virus.

Figure 2

Mean CD4-positive T-Cell counts in groups inoculated with PLV or medium only on day 0. Solid diamonds represent the PLV-inoculated group and open boxes represent the medium-inoculated controls. Arrow indicates inoculation of 5 animals from each group with FIV or diluent. Solid triangles represent the single virus inoculated group (FIV only) and shaded circles represent the dual virus inoculated group. Asterisks indicate a statistically significant difference (p≤0.05) from baseline values.

Figure 3

FIV Infection. FIV copy number per 1 million PBMCs (A) and FIV copy number per milliliter of plasma (B) as measured by PCR in individual animals inoculated with PLV on day 0 followed by FIV on day 28 (shaded circles) or medium only on day 0 followed by FIV on day 28 (solid triangles). Asterisk indicate the single time point at which the higher copy number in the FIV only group were statistically significantly higher than in the group inoculated with PLV prior to FIV.

Figure 4

Serum Neutralizing Antibody (SN) titer measured 59 days post PLV inoculation in individual animals inoculated with PLV on day 0 followed by FIV on day 28 (circles), medium only on day 0 followed by FIV on day 28 (triangles), PLV on day 0 followed by 0.9% NaCl on day 28 (diamonds) or medium only on day 0 followed by 0.9% NaCl on day 28 (squares). There was no statistically significant difference between groups.

Figure 5

Lymphocyte blastogenesis response to mitogen or antigen as measured by incorporation of ³H thymidine. PBMCs were stimulated in triplicate with 1 μg of inactivated PLV or FIV for 4 days or with 1.5 μg Con A for 3 or 4 days prior to incubation in the presence of ³H thymidine and harvest. Stimulation indices (SI) were calculated by dividing the average count for each agent by that of the average count for unstimulated cells. Group mean SI are shown for A) mitogen B) PLV or C) FIV in groups inoculated with PLV or medium only on day 0. Solid diamonds represent the PLV-inoculated group and open boxes represent the medium-inoculated controls. Arrow indicates inoculation of 5 animals from each group with FIV or diluent. Solid triangles represent the single virus inoculated group (FIV only) and shaded circles represent the dual virus inoculated (PLV followed by FIV) group. As indicated by an asterisk, the only statistically significant difference was in Con A response on Day 59 in the PLV only group (SI of 23) was compared to the control group (SI of 5).

Figure 6

IFN-γ expression was measured by real time PCR. Level of expression relative to that of the control group is shown as group means for groups inoculated with PLV or medium only on day 0. Solid diamonds represent the PLV-inoculated group. Arrow indicates inoculation of 5 animals from each group with FIV or diluent. Solid triangles represent the single virus inoculated group (FIV only) and shaded circles represent the dual virus inoculated (PLV followed by FIV) group. Asterisks indicate statistically significant differences (p ≤0.05) from the control group. The number of samples tested for each group at each time point was 10 (before day 28) or 5 (after day 28) with the following exceptions: day 3 n = 8 for control, day 10 n = 9 for control, day 17 n = 8 for control, day 31 n = 3 for control and n = 4 for FIV.

Figure 7

Mean neutrophil counts in groups inoculated with PLV or medium only on day 0. Solid diamonds represent the PLV-inoculated group and open boxes represent the medium-inoculated controls. Arrow indicates inoculation of 5 animals from each group with FIV or diluent. Solid triangles represent the single virus inoculated group (FIV only) and shaded circles represent the dual virus inoculated (PLV followed by FIV) group. Asterisks indicate a statistically significant difference (p≤0.05) from baseline value.