Nasal-associated lymphoid tissue is a mucosal inductive site for virus-specific humoral and cellular immune responses

Peyer's patches are known as mucosal inductive sites for humoral and cellular immune responses in the gastrointestinal tract. In contrast, functionally equivalent structures in the respiratory tract remain elusive. It has been suggested that nasal-associated lymphoid tissue (NALT) might serve as a mucosal inductive site in the upper respiratory tract. However, typical signs of mucosal inductive sites like development of germinal center reactions after Ag stimulation and isotype switching of naive B cells to IgA production have not been directly demonstrated. Moreover, it is not known whether CTL can be generated in NALT. To address these issues, NALT was structurally and functionally analyzed using a model of intranasal infection of C3H mice with reovirus. FACS and histological analyses revealed development of germinal centers in NALT in parallel with generation and expansion of IgA(+) and IgG2a(+) B cells after intranasal reovirus infection. Reovirus-specific IgA was produced in both the upper respiratory and the gastrointestinal tract, whereas production of reovirus-specific IgG2a was restricted to NALT, submandibular, and mesenteric lymph nodes. Moreover, virus-specific CTL were detected in NALT. Limiting dilution analysis showed a 5- to 6-fold higher precursor CTL frequency in NALT compared with a cervical lymph node. Together these data provide direct evidence that NALT is a mucosal inductive site for humoral and cellular immune responses in the upper respiratory tract.     

Long-Term CD4 Th1 and Th2 Memory following Acute Lymphocytic Choriomeningitis Virus Infection

CD4 T cells play a central role in viral immunity. They provide help for B cells and CD8 T cells and can act as effectors themselves. Despite their importance, relatively little is known about the magnitude and duration of virus-specific CD4 T-cell responses. In particular, it is not known whether both CD4 Th1 memory and CD4 Th2 memory can be induced by viral infections. To address these issues, we quantitated virus-specific CD4 Th1 (interleukin 2 [IL-2] and gamma-interferon) and Th2 (IL-4) responses in mice acutely infected with lymphocytic choriomeningitis virus (LCMV). Using two sensitive assays (enzyme-linked immunospot assay and intracellular stain) to measure cytokine production at the single-cell level, we found that both CD4 Th1 and Th2 responses were induced during primary LCMV infection. At the peak (day 8) of the response, the frequency of LCMV-specific CD4 Th1 cells was 1/35 to 1/160 CD4 T cells, and the frequency of Th2 cells was 1/400. After viral clearance, the numbers of virus-specific CD4 T cells dropped to 1/260 to 1/3,700 and then were maintained at this level indefinitely. Upon rechallenge with LCMV, both CD4 Th1 and Th2 memory cells made an anamnestic response in vivo. These results show that unlike some microbial infections in which only Th1 or Th2 responses are seen, an acute viral infection can induce a mixed CD4 T-cell response with long-term memory.     

CD40 ligand-deficient mice generate a normal primary cytotoxic T-lymphocyte response but a defective humoral response to a viral infection.

CD40 ligand is expressed on activated T cells and interacts with CD40 on B cells and monocytes. It is not known what role CD40 ligand plays in the generation of immune responses to viral infection. To address this issue, we examined virus-specific T- and B-cell responses in CD40 ligand-deficient (CD40L-/-) mice following infection with lymphocytic choriomeningitis virus (LCMV). We found that primary anti-LCMV specific antibody responses were severely impaired in CD40L-/- mice, with the defect being most striking for antibody of the immunoglobulin G1 (IgG1) isotype. Interestingly, low levels of LCMV-specific antibodies of the IgG2a, IgG2b, and IgG3 isotypes were made in the CD40L-/- mice, showing that IgG1 responses are totally dependent on CD40L but that at least some IgG2a, IgG2b, and IgG3 responses can be CD40L independent. However, unlike CD40L+/+ mice, CD40L-/- mice were unable to sustain virus-specific antibody responses and showed a gradual decline in serum antibody levels over time. The CD40L-/- mice were also deficient in the generation of memory B cells. In contrast to the severely impaired humoral responses, CD40L-/- mice generated potent virus-specific CD8+ cytotoxic T-lymphocyte responses after LCMV infection and were able to clear the virus. These results show that CD40L does not play a role in generating primary virus-specific CD8+ cytotoxic T-lymphocyte responses but does affect the primary antibody response and the generation of memory B cells.     

Antibody to a lytic cycle viral protein decreases gammaherpesvirus latency in B-cell-deficient mice

While antiviral antibody plays a key role in resistance to acute viral infection, the contribution of antibody to the control of latent virus infection is less well understood. Gammaherpesvirus 68 (gammaHV68) infection of mice provides a model well suited to defining contributions of specific immune system components to the control of viral latency. B cells play a critical role in regulating gammaHV68 latency, but the mechanism(s) by which B cells regulate latency is not known. In the experiments reported here, we determined the effect of passively transferred antibody on established gammaHV68 latency in B-cell-deficient (B-cell(-/-)) mice. Immune antibody decreased the frequency of cells reactivating ex vivo from latency in splenocytes (>10-fold) and peritoneal cells (>100-fold) and the frequency of cells carrying latent viral genome in splenocytes (>5-fold) and peritoneal cells (>50-fold). This effect required virus-specific antibody and was observed when total and virus-specific serum antibody concentrations in recipient B-cell(-/-) mice were <8% of those in normal mice during latent infection. Passive transfer of antibody specific for the lytic cycle gammaHV68 RCA protein, but not passive transfer of antibody specific for the v-cyclin protein or the latent protein M2, decreased both the frequency of cells reactivating ex vivo from latency and the frequency of cells carrying the latent viral genome. Therefore, antibody specific for lytic cycle viral antigens can play an important role in the control of gammaherpesvirus latency in immunocompromised hosts. Based on these findings, we propose a model in which ongoing productive replication is essential for maintaining high levels of latently infected cells in immunocompromised hosts. We confirmed this model by the treatment of latently infected B-cell(-/-) mice with the antiviral drug cidofovir.     

The immunogenicity of intracerebral virus infection depends on anatomical site.

The brain parenchyma affords immune privilege to tissue grafts, but it is not known whether the same is true for intracerebral viral infections. Using stereotactically guided microinjection, we have confined infection with influenza virus A/NT/60/68 to either the brain parenchyma or the cerebrospinal fluid (CSF). A/NT/60/68 infection in the CSF elicited a comparable immune response to intranasal infection, with the production of antiviral serum antibody, priming of antiviral cytotoxic T-cell precursors, and an antiviral proliferative response in the draining lymph nodes. The response to virus in the CSF was detectable sooner after inoculation than the response to intranasal virus and also involved a prolonged production of virus-specific immunoglobulin A in the CSF. In contrast, there was no detectable immune response to virus infection in the brain parenchyma by any of the parameters measured for at least 10 days after inoculation. Over the next 80 days, 46% of the mice given parenchymal virus developed low-level immune responses that did not involve CSF antibody production, while the remaining 54% had no detectable response at any time. Thus, a virus infection confined to the parenchymal substance of the brain primed the immune system inefficiently or not at all.     

Requirement for Fc Effector Mechanisms in the APOBEC3/Rfv3-Dependent Neutralizing Antibody Response

Antiretroviral neutralizing antibody (NAb) responses are often evaluated in the absence of Fc-dependent immune effectors. In murine Friend retrovirus infection, Apobec3/Rfv3 promotes a potent polyclonal NAb response. Here, we show that the Apobec3/Rfv3-dependent NAb response correlated with virus-specific IgG2 titers and that the in vivo neutralization potency of Apobec3/Rfv3-resistant antisera was dependent on activating Fcγ receptors but not complement. The data strengthen retroviral vaccine strategies aimed at eliciting NAbs that activate specific Fcγ receptors.     

Independent regulation of lymphocytic choriomeningitis virus-specific T cell memory pools: relative stability of CD4 memory under conditions of CD8 memory T cell loss

Infection of mice with a series of heterologous viruses causes a reduction of memory CD8(+) T cells specific to viruses from earlier infections, but the fate of the virus-specific memory CD4(+) T cell pool following multiple virus infections has been unknown. We have previously reported that the virus-specific CD4(+) Th precursor (Thp) frequency remains stable into long-term immunity following lymphocytic choriomeningitis virus (LCMV) infection. In this study, we questioned whether heterologous virus infections or injection with soluble protein CD4 Ags would impact this stable LCMV-specific CD4(+) Thp memory pool. Limiting dilution analyses for IL-2-producing cells and intracellular cytokine staining for IFN-gamma revealed that the LCMV-specific CD4(+) Thp frequency remains relatively stable following multiple heterologous virus infections or protein Ag immunizations, even under conditions that dramatically reduce the LCMV-specific CD8(+) CTL precursor frequency. These data indicate that the CD4(+) and CD8(+) memory T cell pools are regulated independently and that the loss in CD8(+) T cell memory following heterologous virus infections is not a consequence of a parallel loss in the memory CD4(+) T cell population.     

Serum antibody response and nasal lymphoid tissue (NALT) structure in the absence of IL-4 or IFN-gamma

Immunization via the nasal route is effective for inducing not only mucosal immunity but also antibody (Ab) response in serum. Nasal lymphoid tissue (NALT) is important for induction of systemic immunity. It remains controversial which T effector cell response is important for serum Ab response after nasal immunization. We investigated serum Ab responses and NALT structures in interleukin (IL)-4 gene targeted (IL-4(-/-)) and interferon (IFN)-gamma gene targeted (IFN-gamma(-/-)) mice. Mice were immunized via nostrils with ovalbumin (OVA) and cholera toxin as adjuvant and serum Ab titers were measured 1 week after final antigen challenge. OVA-specific IgG titers in sera of IL-4(-/-) mice indicated a Th(1) type response, whereas titers in IFN-gamma(-/-) mice and wild-type mice indicated a Th(2) type response. Enhanced serum Ab responses were observed in IL-4(-/-) mice but not IFN-gamma(-/-) mice. OVA-specific Ab-forming cells were detected in the cervical draining lymph nodes but were rare or absent in and around the NALT of all strains of mice. Numbers of OVA-specific Ab-forming cells in cervical lymph nodes were significantly higher in IL-4(-/-) mice than in wild-type and IFN-gamma(-/-) mice. Germinal centers of lymphoid follicles were present in NALT of IL-4(-/-) and other mice. Immunohistochemistry for B and T cell markers revealed that NALT of all mice had approximately the same cellular compositions. Although the absence of IL-4 had no effect on NALT structure, IL-4 may suppress induction of serum Ab responses by nasal immunization.     

Aryl hydrocarbon receptor activation impairs the priming but not the recall of influenza virus-specific CD8+ T cells in the lung

The response of CD8+ T cells to influenza virus is very sensitive to modulation by aryl hydrocarbon receptor (AhR) agonists; however, the mechanism underlying AhR-mediated alterations in CD8+ T cell function remains unclear. Moreover, very little is known regarding how AhR activation affects anamnestic CD8+ T cell responses. In this study, we analyzed how AhR activation by the pollutant 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) alters the in vivo distribution and frequency of CD8+ T cells specific for three different influenza A virus epitopes during and after the resolution of a primary infection. We then determined the effects of TCDD on the expansion of virus-specific memory CD8+ T cells during recall challenge. Adoptive transfer of AhR-null CD8+ T cells into congenic AhR(+/+) recipients, and the generation of CD45.2AhR(-/-)-->CD45.1AhR(+/+) chimeric mice demonstrate that AhR-regulated events within hemopoietic cells, but not directly within CD8+ T cells, underlie suppressed expansion of virus-specific CD8+ T cells during primary infection. Using a dual-adoptive transfer approach, we directly compared the responsiveness of virus-specific memory CD8+ T cells created in the presence or absence of TCDD, which revealed that despite profound suppression of the primary response to influenza virus, the recall response of virus-specific CD8+ T cells that form in the presence of TCDD is only mildly impaired. Thus, the delayed kinetics of the recall response in TCDD-treated mice reflects the fact that there are fewer memory cells at the time of reinfection rather than an inherent defect in the responsive capacity of virus-specific memory CD8+ cells.     

Antiviral CD4 and CD8 T-cell memory: differences in the size of the response and activation requirements

Following acute lymphocytic choriomeningitis virus (LCMV) infection, there is a potent antiviral CD8 T-cell response that eliminates the infection. This initial CD8 T-cell response is followed by a period of memory during which elevated numbers of virus-specific CD8 T cells remain in the mouse. CD4 T cells are also activated after LCMV infection, but relatively less is known about the magnitude and duration of the CD4 response. In this study, we used intracellular staining for interferon-gamma to measure both CD4 and CD8 responses in the same mice at the single cell level. After LCMV infection, there was an increase in the number of activated CD4 T cells and an associated increase in the number of virus-specific CD4 T cells. At the peak of this expansion phase, the frequency of virus-specific CD4 T cells was 1 in 20 (0.5-1.0 x 10(6) per spleen). Like the CD8 response, long-term CD4 memory could be found up to a year after the infection with frequencies of approximately 1 in 260 (0.5-1.5 x 10(5) per spleen). However, the magnitude of virus-specific CD8 T cells was greater than virus-specific CD4 T cells during all phases of the immune response (expansion, death, and memory). At day 8, there were 20- to 35-fold more virus-specific CD8 T cells than CD4 T cells. This initial difference in cell number lasted into the memory phase as there remained a ten- to 20-fold difference in the CD8 and CD4 responses. These results highlight the importance of the expansion phase in determining the size of the memory T-cell pool. In addition to the difference in the magnitude, the activation requirements of CD8 and CD4 T-cell responses were different: CD8 T responses were not affected by blockade of CD40-CD40 ligand interaction whereas CD4 responses were reduced 90%. So while there is long-term memory in both the CD8 and CD4 compartments, the rules regulating the activation of CD8 and CD4 T cells and the overall magnitude of the responses are different.     

CD4+ T cell priming accelerates the clearance of Sendai virus in mice, but has a negative effect on CD8+ T cell memory

Current vaccines designed to promote humoral immunity to respiratory virus infections also induce potent CD4+ T cell memory. However, little is known about the impact of primed CD4+ T cells on the immune response to heterologous viruses that are serologically distinct, but that share CD4+ T cell epitopes. In addition, the protective capacity of primed CD4+ T cells has not been fully evaluated. In the present study, we addressed these two issues using a murine Sendai virus model. Mice were primed with an HN421-436 peptide that represents the dominant CD4+ T cell epitope on the hemagglutinin-neuraminidase (HN) of Sendai virus. This vaccination strategy induced strong CD4+ T cell memory to the peptide, but did not induce Abs specific for the Sendai virus virion. Subsequent Sendai virus infection of primed mice resulted in 1) a substantially accelerated virus-specific CD4+ T cell response in the pneumonic lung; 2) enhanced primary antiviral Ab-forming cell response in the mediastinal lymph nodes; and 3) accelerated viral clearance. Interestingly, the virus-specific CD8+ T cell response in the lung and the development of long-term memory CD8+ T cells in the spleen were significantly reduced. Taken together, our data demonstrate that primed CD4+ T cells, in the absence of pre-existing Ab, can have a significant effect on the subsequent immune responses to a respiratory virus infection.     

Recognition of H-2Kb mutant target cells by Moloney virus-specific cytotoxic T lymphocytes from bm13 (H-2Db mutant) mice. I. Full recognition of Kbm11 by Kb-restricted CTL

In C57BL/6 (B6, H-2b) mice, the secondary in vitro CTL response against Moloney leukemia virus is restricted and regulated by the H-2Db locus. B6.C-H- 2bm13 ( bm13 ) mice, however, carrying a mutation at the Db locus, show an increased H-2Kb-restricted CTL response without a demonstrable CTL component restricted by the mutant Dbm13 molecule (D----K shift). These purely Kb-restricted bm13 virus-specific CTL were incubated with a series of Kb mutant virus-infected target cells to study the effect of the mutations at the target cell level. Of six Kb-mutant virus-infected target cells tested, bm1 cells were not recognized and bm8 cells were recognized only marginally by bm13 virus-specific CTL, whereas bm3 , bm5 , bm6 , and bm11 cells were fully recognized. Thus, the bm3 , bm5 , bm6 , and bm11 Kb mutants fully share the relevant H-2K restriction specificities with H-2Kb, whereas the bm1 mutant totally and the bm8 mutant almost completely lack these specificities. This result differs markedly from the restriction site relationships among B6 and these Kb mutants in other antigenic systems. The most striking example concerns the bm11 mutant, which is fully recognized by Moloney-specific CTL, but not at all by Sendai, minor H (H-3.1, H-4.2), and sulfhydryl hapten-specific CTL. Monoclonal anti-H-2Kb antibody B8-3-24 inhibited virus-specific lysis by bm13 CTL of all Kb virus-infected mutant target cells to which this antibody binds. Lysis of bm5 and bm11 but not of bm3 target cells was inhibited, in line with the fact that B8-3-24 antibody does not bind bm3 . On the other hand, not only bm5 and bm11 but also bm3 virus-infected target cells blocked virus-specific lysis to the same extent as syngeneic bm13 target cells. Therefore, bm13 virus-specific CTL populations do not recognize the discrete cluster alteration in the Kbm3 molecule, as identified by antibody B8-3-24. The bm1 and the bm8 mutations, which have structural alterations in completely different sites of the Kb molecule, show complete or almost complete loss, respectively, of Kb-Moloney restriction sites. This finding supports the notion that these virus-specific CTL recognize conformational determinants rather than linear amino acid sequences.     

Role of CXC chemokine ligand 13, CC chemokine ligand (CCL) 19, and CCL21 in the organization and function of nasal-associated lymphoid tissue

Nasal-associated lymphoid tissue (NALT) orchestrates immune responses to Ags in the upper respiratory tract. Unlike other lymphoid organs, NALT develops independently of lymphotoxin-alpha (LTalpha). However, the structure and function of NALT are impaired in Ltalpha(-/-) mice, suggesting a link between LTalpha and chemokine expression. In this study we show that the expression of CXCL13, CCL19, CCL21, and CCL20 is impaired in the NALT of Ltalpha(-/-) mice. We also show that the NALT of Cxcl13(-/-) and plt/plt mice exhibits some, but not all, of the structural and functional defects observed in the NALT of Ltalpha(-/-) mice. Like the NALT of Ltalpha(-/-) mice, the NALT in Cxcl13(-/-) mice lacks follicular dendritic cells, BP3(+) stromal cells, and ERTR7(+) lymphoreticular cells. However, unlike the NALT of Ltalpha(-/-) mice, the NALT of Cxcl13(-/-) mice has peripheral node addressin(+) high endothelial venules (HEVs). In contrast, the NALT of plt/plt mice is nearly normal, with follicular dendritic cells, BP3(+) stromal cells, ERTR7(+) lymphoreticular cells, and peripheral node addressin(+) HEVs. Functionally, germinal center formation and switching to IgA are defective in the NALT of Ltalpha(-/-) and Cxcl13(-/-) mice. In contrast, CD8 T cell responses to influenza are impaired in Ltalpha(-/-) mice and plt/plt mice. Finally, the B and T cell defects in the NALT of Ltalpha(-/-) mice lead to delayed clearance of influenza from the nasal mucosa. Thus, the B and T cell defects in the NALT of Ltalpha(-/-) mice can be attributed to the impaired expression of CXCL13 and CCL19/CCL21, respectively, whereas impaired HEV development is directly due to the loss of LTalpha.     

Anatomical and cellular requirements for the activation and migration of virus-specific CD8+ T cells to the brain during Theiler's virus infection

Theiler's murine encephalomyelitis virus (TMEV) infection of the brain induces a virus-specific CD8(+) T-cell response in genetically resistant mice. The peak of the immune response to the virus occurs 7 days after infection, with an immunodominant CD8(+) T-cell response against a VP2-derived capsid peptide in the context of the D(b) molecule. The process of activation of antigen-specific T cells that migrate to the brain in the TMEV model has not been defined. The site of antigenic challenge in the TMEV model is directly into the brain parenchyma, a site that is considered immune privileged. We investigated the hypothesis that antiviral CD8(+) T-cell responses are initiated in situ upon intracranial inoculation with TMEV. To determine whether a brain parenchymal antigen-presenting cell is responsible for the activation of virus-specific CD8(+) T cells, we evaluated the CD8(+) T-cell response to the VP2 peptide in bone marrow chimeras and mutant mice lacking peripheral lymphoid organs. The generation of the anti-TMEV CD8(+) T-cell response in the brain requires priming by a bone marrow-derived antigen-presenting cell and the presence of peripheral lymphoid organs. Although our results show that activation of TMEV-specific CD8(+) T cells occurs in the peripheral lymphoid compartment, they do not exclude the possibility that the immune response to TMEV is initiated by a brain-resident, bone marrow-derived, antigen-presenting cell.     

Episodic occurrence of antibodies against the bovine leukemia virus Rex protein during the course of infection in sheep.

Infection by bovine leukemia virus (BLV) is characterized by a long clinical latency after which some individuals develop B-cell tumors. The contributions of the viral regulatory proteins Tax and Rex during clinical latency and disease are incompletely understood. To learn about Rex expression in the host, we used a sensitive immunoprecipitation assay to detect Rex antibodies throughout the course of BLV infection in sheep. Sixty percent of the infected animals produced Rex antibodies in intermittent episodes. This pattern differed markedly from that of antibodies to virion structural proteins, which were maintained in all animals throughout infection. Only one of two animals that developed tumors had detectable Rex antibodies at the time, although the other had previously demonstrated an especially strong Rex antibody response. We examined the Rex response in the context of BLV infection by comparing it with the frequency of circulating mononuclear blood cells that could transcribe BLV RNA or produce infectious virus. Episodes of Rex antibody occurrence followed some but not all increases in the number of BLV-transcribing cells. Since the appearance of circulating antibodies requires that the intracellular Rex protein be available to serve as antigen, the episodic pattern of occurrence of Rex antibodies could result from intermittent killing by virus-specific cytotoxic cells. Fluctuations in titer that were observed during some episodes of Rex response could be due to antibody retention by antigen present in lymphoid tissue.     

Cutting edge: Uniqueness of lymphoid chemokine requirement for the initiation and maturation of nasopharynx-associated lymphoid tissue organogenesis

CD3(-)CD4(+)CD45(+) inducer cells are required for the initiation of mucosa-associated organogenesis of both nasopharynx-associated lymphoid tissues (NALT) and Peyer's patches (PP) in the aerodigestive tract. CXCL13(-/-) mice and mice carrying the paucity of lymph node T cell (plt) mutation and lacking expression of CCL19 and CCL21 accumulate CD3(-)CD4(+)CD45(+) cells at the site of NALT but not of PP genesis. Although NALT was observed to develop in adult CXCL13(-/-) and plt/plt mice, the formation of germinal centers in CXCL13(-/-) mice was affected, and their population of B cells was much lower than in the NALT of CXCL13(+/-) mice. Similarly, fewer T cells were observed in the NALT of plt/plt mice than in control mice. These findings indicate that the initiation of NALT organogenesis is independent of CXCL13, CCL19, and CCL21. However, the expression of these lymphoid chemokines is essential for the maturation of NALT microarchitecture.     

Analysis of the human T-cell response to picornaviruses: identification of T-cell epitopes close to B-cell epitopes in poliovirus.

Little is known about the nature and specificity of T-cell-mediated responses to picornaviruses in humans. In this study, the nature of the T-cell response to seven picornaviruses, including polioviruses, coxsackieviruses B3 and B4, human rhinovirus 14, and encephalomyocarditis virus, was determined. Twenty-nine individuals responded to poliovirus type 3, coxsackievirus B3, and encephalomyocarditis virus by proliferation of T cells, and from such cultures, 130 virus-specific T-cell lines were established. T-cell lines generated in response to encephalomyocarditis virus were exclusively strain specific. However, the majority of T-cell lines established in response to viruses, other than encephalomyocarditis virus, were cross-reactive to each other. Their cross-reactivity was confirmed in 2 of the 30 picornavirus-specific clonally derived T-cell lines from two subjects, but the majority of these lines were serotype specific. T-cell epitopes adjacent to each of the B-cell antigenic sites in VP1 of poliovirus type 3 were identified. The response to the region adjacent to B-cell antigenic site 1 (residues 97 to 114) was dominant between individuals. The localization of this major CD4 T-cell epitope may permit the construction of chimeric viruses utilizing the natural picornavirus T-cell response to augment production of antibody specific for inserted sequences.     

Cutting edge: activation of virus-specific CD4 T cells throughout γ-herpesvirus latency

CD4 T cells are essential for immune control of γ-herpesvirus latency. We previously identified a murine MHC class II-restricted epitope in γ-herpesvirus-68 gp150 (gp150(67-83)I-A(b)) that elicits CD4 T cells that are maintained throughout long-term infection. However, it is unknown whether naive cells can be recruited into the antiviral CD4 T cell pool during latency. In this study, we generate a mouse transgenic for a gp150-specific TCR and show epitope-specific activation of transgenic CD4 T cells during acute and latent infections. Furthermore, although only dendritic cells can stimulate virus-specific CD8 T cells during latency, we show that both dendritic cells and B cells stimulate transgenic CD4 T cells. These studies demonstrate that naive CD4 T cells specific for a viral glycoprotein can be stimulated throughout infection, even during quiescent latency, suggesting that CD4 T cell memory is maintained in part by the continual recruitment of naive cells.     

Roles of target cells and virus-specific cellular immunity in primary simian immunodeficiency virus infection

There is an ongoing debate on whether acute human immunodeficiency virus infection is controlled by target cell limitation or by virus-specific cellular immunity. To resolve this question, we developed a novel mathematical modeling scheme which allows us to incorporate measurements of virus load, target cells, and virus-specific immunity and applied it to a comprehensive data set generated in an experiment involving rhesus macaques infected with simian immunodeficiency virus. Half of the macaques studied were treated during the primary infection period with reagents which block T-cell costimulation and as a result displayed severely impaired virus-specific immune responses. Our results show that early viral replication in normal infection is controlled to a large extent by virus-specific CD8(+) T cells and not by target cell limitation.     

Post-exposure vaccination improves gammaherpesvirus neutralization

Herpesvirus carriers transmit infection despite making virus-specific antibodies. Thus, their antibody responses are not necessarily optimal. An important question for infection control is whether vaccinating carriers might improve virus neutralization. The antibody response to murine gamma-herpesvirus-68 (MHV-68) blocks cell binding, but fails to block and even enhances an IgG Fc receptor-dependent infection of myeloid cells. Viral membrane fusion therefore remains intact. Although gH/gL-specific monoclonal antibodies can block infection at a post-binding step close to membrane fusion, gH/gL is a relatively minor antibody target in virus carriers. We show here that gH/gL-specific antibodies can block both Fc receptor-independent and Fc receptor-dependent infections, and that vaccinating virus carriers with a gH/gL fusion protein improves their capacity for virus neutralization both in vitro and in vivo. This approach has the potential to reduce herpesvirus transmission.