Rapid virus dissemination in infant macaques after oral simian immunodeficiency virus exposure in the presence of local innate immune responses

Abstract

A vaccine to protect human immunodeficiency virus (HIV)-exposed infants is an important goal in the global fight against the HIV pandemic. Two major challenges in pediatric HIV vaccine design are the competence of the neonatal/infant immune system in comparison to the adult immune system and the frequent exposure to HIV via breast-feeding. Based on the hypothesis that an effective vaccine needs to elicit antiviral immune responses directly at the site of virus entry, the pattern of virus dissemination in relation to host immune responses was determined in mucosal and lymphoid tissues of infant macaques at 1 week after multiple oral exposures to simian immunodeficiency virus (SIV). The results show that SIV disseminates systemically by 1 week. Infant macaques can respond rapidly to virus challenge and mount strong innate immune responses. However, despite systemic infection, these responses are most pronounced in tissues close to the viral entry site, with the tonsil being the primary site of virus replication and induction of immune responses. Thus, distinct anatomic compartments are characterized by unique cytokine gene expression patterns. Importantly, the early response at mucosal entry sites is dominated by the induction of proinflammatory cytokines, while cytokines with direct antiviral activity, alpha/beta interferons, are only minimally induced. In contrast, both antiviral and proinflammatory cytokines are induced in lymphoid tissues. Thus, although infant macaques can respond quickly to oral viral challenge, the locally elicited immune responses at mucosal entry sites are likely to favor immune activation and thereby virus replication and are insufficient to limit virus replication and dissemination.

FIG. 1.

Plasma and tissue vRNA levels. (A) Log₁₀ vRNA copies per microgram of tissue RNA or per milliliter of plasma for individual monkeys in distinct anatomic locations at 1 week after the first virus exposure. Each symbol represents an individual animal. Tissues of the oral mucosa and draining LN are shown in red; gut-associated tissues, including the mesenteric LN, are depicted in blue; and distal lymphoid tissues and plasma are shown in black. (B) vRNA levels in various tissues in individual animals. The tissue color scheme is the same as for panel A. Animals are listed on the x axis in the order of their plasma vRNA levels, from lowest to highest.

FIG. 2.

Type I IFN response at 1 week p.i. Panels A, B, and C show the increase in mRNA levels for IFN-α, Mx, and CXCL10, respectively, in various tissues at 1 week p.i. compared to average mRNA levels of the same cytokines in the same tissues of uninfected infant macaques. Tissues are abbreviated as follows: G, gingiva; T, tonsil; S-LN, submandibular LN; E, esophagus; J, jejunum; C, colon; M-LN, mesenteric LN; A-LN, axillary LN; SPL, spleen. The color coding is the same as in Fig. 1. An asterisk at the top of a tissue column indicates that the increase in cytokine mRNA levels in this tissue is significantly (P < 0.05) higher than in other tissues (see the text for details).

FIG. 3.

Inflammatory response at 1 week p.i. in tissues of SIV-infected infant macaques. Panels A, B, and C show the increase in MIP-1α, IL-12, and IL-6 mRNA levels, respectively, in various tissues at 1 week p.i. compared to average mRNA levels of the same cytokines in the same tissues of uninfected infant macaques. Abbreviations are as in Fig. 2. An asterisk at the top of a tissue column indicates that the increase in cytokine mRNA levels in this tissue is significantly (P < 0.05) higher than in other tissues (see the text for details).

FIG. 4.

IFN-γ-mediated responses. Panels A and B show the increase in IFN-γ and Mig/CXCL9 mRNA levels, respectively, in various tissues at 1 week p.i. compared to average mRNA levels of the same cytokines in the same tissues of uninfected infant macaques. Panels C and D show perforin and granzyme mRNA levels, respectively, in various tissues at 1 week p.i. compared to average mRNA levels of the same cytokines in the same tissues of uninfected infant macaques. Abbreviations are as in Fig. 2. An asterisk at the top of a tissue column indicates that the increase in cytokine mRNA levels in this tissue is significantly (P < 0.05) higher than in other tissues (see the text for details).

FIG. 5.

PBMC responses at 1 week after oral SIV exposure in infant macaques. (A) Relationship between plasma vRNA levels and PBMC mRNA levels for the IFN-stimulated genes Mx and CXCL10 and the chemokine MIP-1α. (B) Increase in PBMC mRNA levels for the Th1 cytokine IFN-γ and the Th2 cytokine IL-4 for each of the SIV-infected animals relative to the IFN-γ and IL-4 PBMC mRNA levels of eight SIV-naïve animals. Animals are listed on the x axis in the order of their plasma vRNA levels, from lowest to highest.