Temporal and anatomic relationship between virus replication and cytokine gene expression after vaginal simian immunodeficiency virus infection

Abstract

The current knowledge about early innate immune responses at mucosal sites of human immunodeficiency virus (HIV) entry is limited but likely to be important in the design of effective HIV vaccines against heterosexual transmission. This study examined the temporal and anatomic relationship between virus replication, lymphocyte depletion, and cytokine gene expression levels in mucosal and lymphoid tissues in a vaginal-transmission model of HIV in rhesus macaques. The results of the study show that the kinetics of cytokine gene expression levels in the acute phase of infection are positively correlated with virus replication in a tissue. Thus, cytokine responses after vaginal simian immunodeficiency virus (SIV) inoculation are earliest and strongest in mucosal tissues of the genital tract and lowest in systemic lymphoid tissues. Importantly, the early cytokine response was dominated by the induction of proinflammatory cytokines, while the induction of cytokines with antiviral activity, alpha/beta interferon, occurred too late to prevent virus replication and dissemination. Thus, the early cytokine response favors immune activation, resulting in the recruitment of potential target cells for SIV. Further, unique cytokine gene expression patterns were observed in distinct anatomic locations with a rapid and persistent inflammatory response in the gut that is consistent with the gut being the major site of early CD4 T-cell depletion in SIV infection.

FIG. 1.

Viral RNA levels and IFN-α/β responses in tissues after vaginal SIV infection. (A) Average vRNA levels at various time points after vaginal SIV inoculation for each tissue are shown. Viral RNA levels are reported as log₁₀ vRNA copies per μg tissue RNA. The different tissues are grouped by anatomic location, with tissues of the genital tract shown in red (vaginal mucosa, solid bars; cervix, striped bars; genital lymph nodes [LN], open bars), tissues of the gut in black (colon, solid bars; jejunum, striped bars; mesenteric LN, open bars), and distal lymphoid tissues (spleen, solid bars; axillary LN, open bars) in blue. The numbers underneath each bar on the x axis indicate the days after SIV inoculation when tissues were collected. (B and C) Increases in IFN-β and IFN-α mRNA levels compared to IFN-β and IFN-α mRNA levels in the same tissues of SIV-naïve animals. The lines above the bars show statistically significant differences in cytokine mRNA levels between tissues connected by the line, with the tissue with statistically higher cytokine mRNA levels compared to the other tissues indicated by an asterisk. The error bars represent SD.

FIG. 2.

Correlation between tissue vRNA levels and IFN-α mRNA levels. Each individual graph shows the log₁₀ increase of IFN-α mRNA levels (y axis) over log₁₀ vRNA copies/μg tissue RNA (x axis) in the same tissue. Data are shown for all animals collected for each tissue throughout the first 28 days p.i. Each symbol represents an individual animal. If significant correlations were determined (P < 0.05; NS = nonsignificant), the correlation efficient (r² value) is also shown.

FIG. 3.

Comparative analysis of proinflammatory cytokine gene expression levels in the genital tract, gut tissues, and distal lymphoid tissues. (A) Increases in TNF-α mRNA levels compared to cytokine mRNA levels in the same tissues of SIV-naïve animals. (B) Increase in IL-6 mRNA levels compared to cytokine mRNA levels in the same tissues of SIV-naïve animals. (C) Increase in MIP-1α mRNA levels compared to cytokine mRNA levels in the same tissues of SIV-naïve animals. See the legend to Fig. 1 for details.

FIG. 4.

Tissue mRNA levels for IFN-γ, IL-8, and IL-12 after vaginal SIV inoculation. (A) Increase in IFN-γ mRNA levels compared to cytokine mRNA levels in the same tissues of SIV-naïve animals. (B) Increase in IL-8 mRNA levels compared to cytokine mRNA levels in the same tissues of SIV-naïve animals. (C) Increase in IL-12 mRNA levels compared to cytokine mRNA levels in the same tissues of SIV-naïve animals. See the legend to Fig. 1 for details.