Rotavirus-specific cytotoxic T lymphocytes appear at the intestinal mucosal surface after rotavirus infection.

The gastrointestinal tract is constantly exposed to a variety of potentially invasive bacteria and viruses. The first line of defense of the host against these pathogens is the intestinal mucosal surface, which consists of epithelial cells, intraepithelial lymphocytes (IELs), mucus, and secretory immunoglobulins. Little is known about the function, memory, or trafficking of IELs after intestinal infection. We found that IELs obtained 6 days after oral inoculation of mice with the intestinal pathogen rotavirus (simian strain RRV) lysed rotavirus-infected target cells; cytotoxic T lymphocytes (CTLs) were responsible for rotavirus-specific cytotoxic activity. Rotavirus-specific cytotoxic activity by IELs was (i) eliminated by treatment with Thy 1.2-specific immunoglobulin M plus complement, (ii) restricted by proteins encoded at the major histocompatibility complex, and (iii) absent in mock-infected animals. Oral inoculation of mice with RRV also induced rotavirus-specific CTLs in splenic and intestinal lymphocytes (mesenteric lymph nodes, Peyer's patch). Parenteral inoculation induced rotavirus-specific CTLs in splenic, intestinal (IELs, mesenteric lymph nodes, Peyer's patch), and nonintestinal lymphocytes (inguinal nodes). Therefore, presentation of rotavirus to the intestinal mucosal surface was not necessary to induce IELs with virus-specific cytotoxic activity. At 4 weeks after oral or parenteral inoculation of mice with RRV, rotavirus-specific CTL precursors appeared among splenic, Peyer's patch, inguinal, and mesenteric node lymphocytes, but not among IELs. IELs with rotavirus-specific cytotoxic activity may be generated from precursors at a site other than the intestinal mucosal surface. Part of the response of the host to enteric infection may include surveillance and lysis of virus-infected villus epithelial cells by IELs.     

Qualitative and quantitative characteristics of rotavirus-specific CD8 T cells vary depending on the route of infection

CD8 T-cell response provides an important defense against rotavirus, which infects a variety of systemic locations in addition to the gut. Here we investigated the distribution, phenotype, and function of rotavirus-specific CD8 T cells in multiple organs after rotavirus infection initiated via the intranasal, oral, or intramuscular route. The highest level of virus-specific CD8 T cells was observed in the Peyer's patches of orally infected mice and in the lungs of intranasally infected animals. Very low levels of virus-specific CD8 T cells were detected in peripheral blood or spleen irrespective of the route of infection. Rotavirus-specific CD8 T cells from Peyer's patches of orally infected mice expressed high levels of CCR9, while CXCR6 and LFA-1 expression was associated with virus-specific CD8 T cells in lungs of intranasally infected mice. Oral infection induced the highest proportion of gamma interferon(-) CD107a/b(+) CD8 T cells in Peyer's patches. When equal numbers of rotavirus-specific CD8 T cells were transferred into Rag-1 knockout mice chronically infected with rotavirus, the donor cells derived from Peyer's patches of orally infected mice were more efficient than those derived from lungs of intranasally infected animals in clearing intestinal infection. These results suggest that different routes of infection induce virus-specific CD8 T cells with distinct homing phenotypes and effector functions as well as variable abilities to clear infection.     

Recovery from chronic rotavirus infection in mice with severe combined immunodeficiency: virus clearance mediated by adoptive transfer of immune CD8+ T lymphocytes.

Severe combined immunodeficient (SCID) mice lack both functional T and B cells. These mice develop chronic rotavirus infection following an oral inoculation with the epizootic diarrhea of infant mice (EDIM) rotavirus. Reconstitution of rotavirus-infected SCID mice with T lymphocytes from immunocompetent mice allows an evaluation of a role of T-cell-mediated immunity in clearing chronic rotavirus infection. Complete rotavirus clearance was demonstrated in C.B-17/scid mice 7 to 9 days after the transfer of immune CD8+ splenic T lymphocytes from histocompatible BALB/c mice previously immunized intraperitoneally with the EDIM-w strain of murine rotavirus. The virus clearance mediated by T-cell transfer was restricted to H-2d-bearing T cells and occurred in the absence of rotavirus-specific antibody as determined by enzyme-linked immunosorbent assay, neutralization, immunohistochemistry, and radioimmunoprecipitation. Temporary clearance of rotavirus was observed after the transfer of immune CD8+ T cells isolated from the intestinal mucosa (intraepithelial lymphocytes [IELs]) or the spleens of BALB/c mice previously infected with EDIM by the oral route. Chronic virus shedding was transiently eliminated 7 to 11 days after spleen cell transfer and 11 to 12 days after IEL transfer. However, recurrence of rotavirus infection was detected 1 to 8 days later in all but one SCID recipient receiving cells from orally immunized donors. The viral clearance was mediated by IELs that were both Thy1+ and CD8+. These data demonstrated that the clearance of chronic rotavirus infection in SCID mice can be mediated by immune CD8+ T lymphocytes and that this clearance can occur in the absence of virus-specific antibodies.     

Relative Importance of Rotavirus-Specific Effector and Memory B Cells in Protection against Challenge

Adult BALB/c mice were orally inoculated with murine (strain EDIM), simian (strain RRV), or bovine (strain WC3) rotavirus. Six or 16 weeks after inoculation, mice were challenged with EDIM. At the time of challenge and in the days immediately following challenge, production of rotavirus-specific immunoglobulin A (IgA), IgG, and IgM by small intestinal lamina propria lymphocytes (LPL) was determined by fragment culture, and quantities of virus-specific antibodies at the intestinal mucosal surface were determined by intestinal lavage. Mice immunized with EDIM were completely protected against EDIM challenge both 6 and 16 weeks after immunization. Protection was associated with production of high levels of IgA by LPL and detection of virus-specific IgA at the intestinal mucosal surface. In addition, animals immunized and later challenged with EDIM did not develop a boost in antibody responses, suggesting that they were also not reinfected. We also found that in mice immunized with nonmurine rotaviruses, (i) quantities of virus-specific IgA generated following challenge were greater 16 weeks than 6 weeks after immunization, (ii) immunization enhanced the magnitude but did not hasten the onset of production of high quantities of virus-specific IgA by LPL after challenge, and (iii) immunization induced partial protection against challenge; however, protection was not associated with either production of virus-specific antibodies by LPL or detection of virus-specific antibodies at the intestinal mucosal surface.     

VP4-specific intestinal antibody response to rotavirus in a murine model of heterotypic infection.

We have adapted a murine model of heterotypic rotavirus infection for the purpose of evaluating the intestinal antibody response to an infection that mimics human vaccination. Neonatal mice were infected with the rhesus rotavirus (RRV). The enzyme-linked immunospot assay was used in order to avoid common artifacts in the quantitation of intestinal immune responses inherent in measurements of luminal or serum immunoglobulins and to obtain easily quantifiable data in a flexible and convenient format. Functionally active lymphocytes were harvested from the spleen, small intestinal lamina propria, Peyer's patches, and mesenteric lymph nodes and processed into single-cell suspensions. Antibody-secreting cells (ASC) were quantitated from 5 to 50 days after infection for total, RRV-specific, baculovirus-expressed VP4-specific, and single-shell RRV-specific ASC secreting either immunoglobulin G (IgG), IgM, or IgA. The response to VP4 constituted less than 1.5% of the total virus-specific response, which was located almost exclusively in the gut and was 90% IgA. Intestinal ASC were directed overwhelmingly toward proteins incorporated in the single-shell particle, predominantly VP2 and VP6. We conclude that the antibody response to VP4, thought to be the site of the important neutralization sites conserved among several rotavirus serotypes, is an extremely small portion of the overall antibody response in the intestinal tract.     

The Magnitude and Specificity of Influenza A Virus-Specific Cytotoxic T-Lymphocyte Responses in Humans Is Related to HLA-A and -B Phenotype

The repertoire of human cytotoxic T-lymphocytes (CTL) in response to influenza A viruses has been shown to be directed towards multiple epitopes, with a dominant response to the HLA-A2-restricted M1(58-66) epitope. These studies, however, were performed with peripheral blood mononuclear cells (PBMC) of individuals selected randomly with respect to HLA phenotype or selected for the expression of one HLA allele without considering an influence of other HLA molecules. In addition, little information is available on the influence of HLA makeup on the overall CTL response against influenza viruses. Here, the influenza A virus-specific CTL response was investigated in groups of HLA-A and -B identical individuals. Between groups the individuals shared two or three of the four HLA-A and -B alleles. After in vitro stimulation of PBMC with influenza virus, the highest CTL activity was found in HLA-A2(+) donors. A similar pattern was observed for the precursor frequency of virus-specific CTL (CTLp) ex vivo, with a higher CTLp frequency in HLA-A2-positive donors than in HLA-A2-negative donors, which were unable to recognize the immunodominant M1(58-66) epitope. In addition, CTL activity and frequency of CTLp for the individual influenza virus epitopes were determined. The frequency of CTLp specific for the HLA-B8-restricted epitope NP(380-388) was threefold lower in HLA-B27-positive donors than in HLA-B27-negative donors. In addition, the frequency of CTLp specific for the HLA-A1-restricted epitope NP(44-52) was threefold higher in HLA-A1-, -A2-, -B8-, and -B35-positive donors than in other donors, which was confirmed by measuring the CTL activity in vitro. These findings indicate that the epitope specificity of the CTL response is related to the phenotype of the other HLA molecules. Furthermore, the magnitude of the influenza virus-specific CTL response seems dependent on the HLA-A and -B phenotypes.     

Migration of antigen-presenting B cells from peripheral to mucosal lymphoid tissues may induce intestinal antigen-specific IgA following parenteral immunization.

Parenterally administered immunizations have long been used to induce protection from mucosal pathogens such as Bordetella pertussis and influenza virus. We previously found that i.m. inoculation of mice with the intestinal pathogen, rotavirus, induced virus-specific Ab production by intestinal lymphocytes. We have now used adoptive transfer studies to identify the cell types responsible for the generation of virus-specific Ab production by gut-associated lymphoid tissue (GALT) after i.m. immunization. Three days after i.m. immunization with rotavirus, cells obtained from the draining peripheral lymph nodes of donor mice were transferred into naive recipient mice. We found that intestinal lymphocytes produced rotavirus-specific Igs (IgM, IgA, and IgG) 2 wk after transfer of either unfractionated cells, or unfractionated cells rendered incapable of cellular division by mitomycin C treatment. Additional studies demonstrated that rotavirus-specific IgA, but not IgG, was produced by intestinal lymphocytes after transfer of purified B cells. Ig allotype analysis revealed that rotavirus-specific IgA was produced by intestinal B cells of recipient origin, suggesting that migration of Ag-presenting B cells from peripheral lymphoid tissues to GALT may contribute to the generation of mucosal IgA responses after parenteral immunization. Strategies that promote Ag uptake and presentation by B cells may enhance mucosal IgA production following parenteral immunization.     

Immunologic correlates of protection against rotavirus challenge after intramuscular immunization of mice.

The capacity of intramuscular (i.m.) inoculation of mice with homologous or heterologous host rotaviruses to induce protection from challenge was evaluated. i.m. inoculation with live, wild-type rotavirus (murine strain EDIM) induced complete protection from viral shedding after challenge for at least 6 weeks after inoculation; protection was correlated with production of virus-specific immunoglobulin A (IgA) by lamina propria (LP) lymphocytes. i.m. inoculation with inactivated EDIM, cell culture-adapted EDIM, or simian strain RRV was associated with partial protection, characterized by reduced viral shedding after challenge. Partial protection after challenge was not associated with production of virus-specific IgA by LP lymphocytes. The mechanisms by which i.m. inoculation induces virus-specific humoral immune responses in the small intestinal LP were examined.     

Effects of antigen-feeding on intestinal and systemic immune responses. I. priming of precursor cytotoxic T cells by antigen feeding.

The ability of antigens administered by the intestinal route to alter the cytotoxic T lymphocyte (CTL) population in intestinal and extraintestinal sites was examined by feeding mice tumor cells bearing H-2 or non-H-2 gene-coded cell surface alloantigenic differences. Peyer's patches from mice fed tumor cells differing at H-2 demonstrated a 12-fold increase in specific CTL activity over controls after stimulation of culture but the precursor CTL population in Peyer's patches was not expanded by feeding mice cells bearing minor H gene coded alloantigenic differences. In contrast, the precursor CTL pool in spleen was increased both in mice fed cells bearing alloantigenic differences coded for by H-2 and non-H-2 gene loci. The precursor CTL population in mesenteric lymph nodes (MN) was not expanded significantly by tumor cell feeding. Feeding was nearly as effective as i.p. priming at expanding the Peyer's patch precursor CTL population when tumor cells bearing H-2 differences were used, whereas i.p. priming was more effective than feeding in expanding the precursor CTL population in spleen.     

Role of immunoglobulin A in protection against reovirus entry into Murine Peyer's patches

Reovirus type 1 Lang (T1L) infects the mouse intestinal mucosa by adhering specifically to epithelial M cells and exploiting M-cell transport to enter the Peyer's patches. Oral inoculation of adult mice has been shown to elicit cellular and humoral immune responses that clear the infection within 10 days. This study was designed to determine whether adult mice that have cleared a primary infection are protected against viral entry upon oral rechallenge and, if so, whether antireovirus secretory immunoglobulin A (S-IgA) is a necessary component of protection. Adult BALB/c mice that were orally inoculated on day 0 with reovirus T1L produced antiviral S-IgA in feces and IgG in serum directed primarily against the reovirus sigma1 attachment protein. Eight hours after oral reovirus challenge on day 21, the Peyer's patches of previously exposed mice contained no detectable virus whereas Peyer's patches of naive controls contained up to 2,300 PFU of reovirus/mg of tissue. Orally inoculated IgA knockout (IgA(-/-)) mice cleared the initial infection as effectively as wild-type mice and produced higher levels of reovirus-specific serum IgG and secretory IgM than C57BL/6 wild-type mice. When IgA(-/-) mice were rechallenged on day 21, however, their Peyer's patches became infected. These results indicate that intestinal S-IgA is an essential component of immune protection against reovirus entry into Peyer's patch mucosa.     

Influenza Virus-Infected Epithelial Cells Present Viral Antigens to Antigen-Specific CD8+ Cytotoxic T Lymphocytes

We have investigated the mechanisms involved in the clearance of viral infection at the epithelium level by analyzing the activity of influenza virus-specific cytotoxic T lymphocytes (CTL) against virus-infected CMT-93 intestinal epithelial cells. Epithelial cells infected with live influenza virus effectively present viral antigens and were lysed by both homotypic and heterotypic influenza virus-specific CD8⁺ T cells. These results shed new light on the control of viral infection through the elimination of virus-infected epithelial cells by virus-specific CTL and demonstrate that CMT-93 cells furnish an appropriate model for in vitro evaluation of CTL activity against virus-infected epithelial cells.     

Abrogation of anti-Pichinde virus cytotoxic T cell memory by cyclophosphamide and restoration by coinfection or interleukin 2

Previously, we demonstrated that memory cell-mediated immune responses can be generated in Pichinde virus (PV)-primed mice after secondary challenge in vivo with homologous virus. Further, treatment of mice with cyclophosphamide (CY) before primary infection with PV abrogated the generation of H-2-restricted, virus-specific cytotoxic T lymphocytes (CTL), and rechallenge of these mice was followed by neither a primary nor a secondary CTL response. Here, we demonstrate that this CY-induced block in memory anti-PV CTL generation was not due to establishment of a persistent infection. Interestingly, this CY-induced block in memory anti-PV CTL generation was overcome by secondarily coinfecting mice with PV and lymphocytic choriomeningitis virus (LCMV) or PV and Tacaribe virus. Secondary infection with LCMV or Tacaribe virus alone did not elicit anti-PV CTL. Coinfection resulted in the generation of a PV-specific memory CTL response as judged by maximal activity on day 4 after rechallenge. Co-infection with PV and vesicular stomatitis virus, an unrelated rhabdovirus, did not efficiently restore memory anti-PV CTL responses. Memory anti-PV CTL responses were also restored when interleukin 2 (IL 2)-containing supernatants were injected i.p. after rechallenge of CY-treated mice with PV. To demonstrate that IL 2 was the responsible lymphokine in these preparations, highly purified IL 2 was added to in vitro cultures of spleen cells from CY-treated PV-primed mice. In the presence of PV-infected syngeneic macrophages, addition of purified IL 2 resulted in a dose-dependent restoration of H-2-restricted anti-PV CTL activity. The CTL precursor (CTLp) frequency of CY-treated PV-primed mice was markedly decreased from that of normal PV-primed mice. Thus, the long-lasting block in the ability to generate a PV-specific memory CTL response after CY treatment appears to be due to both a lack of helper T cell activity and a significant reduction of CTLp. However, this block may be overcome by coinfecting with viruses that cross-react at the helper T cell level or by exogenous treatment with highly purified IL 2.     

Colony-stimulating factor (CSF-1): its enhancement of plasminogen activator production and inhibition of cell growth in a mouse macrophage cell line

The cell-mediated immune response by the gut-associated lymphoid tissues to antigens within the intestinal tract is poorly understood. Our objective was to investigate the antigen-specific T cell proliferative response and cytotoxic T lymphocyte (CTL) response of cells from the GALT after enteric immunization with vaccinia virus. Lymphocytes able to proliferate in the presence of vaccinia virus in vitro were found in large numbers in mesenteric lymph nodes (MLN) 6 days after the injection of vaccinia virus into the lumen of the small bowel. The MLN at this time also contained vaccinia-specific CTL, but unlike the proliferating cells, which were found for several weeks after immunization, the CTL were demonstrable in the MLN for only a few days. Peyer's patches were found to contain neither antigen-stimulated proliferating cells nor CTL. The viral-specific proliferating lymphocytes from the MLN 10 days after immunization were sIg-, monoclonal antibody W3/25+, MRC OX-8- large lymphoblasts. The vaccinia-specific CTL were also large lymphoblasts, but they belonged to the W3/25-, OX-8+ subset. Thus, a strong T helper and cytotoxic T lymphoblast response is generated within the MLN after viral challenge of the gut.     

Japanese encephalitis virus infection induces changes of mRNA profile of mouse spleen and brain

Background

Rotaviruses are the single most important cause of severe diarrhea in young children worldwide. The current study was conducted to assess whether colostrum containing rotavirus-specific antibodies (Gastrogard-R^®) could protect against rotavirus infection. In addition, this illness model was used to study modulatory effects of intervention on several immune parameters after re-infection.

Methods

BALB/c mice were treated by gavage once daily with Gastrogard-R^® from the age of 4 to 10 days, and were inoculated with rhesus rotavirus (RRV) at 7 days of age. A secondary inoculation with epizootic-diarrhea infant-mouse (EDIM) virus was administered at 17 days of age. Disease symptoms were scored daily and viral shedding was measured in fecal samples during the post-inoculation periods. Rotavirus-specific IgM, IgG and IgG subclasses in serum, T cell proliferation and rotavirus-specific delayed-type hypersensitivity (DTH) responses were also measured.

Results

Primary inoculation with RRV induced a mild but consistent level of diarrhea during 3-4 days post-inoculation. All mice receiving Gastrogard-R^® were 100% protected against rotavirus-induced diarrhea. Mice receiving both RRV and EDIM inoculation had a lower faecal-viral load following EDIM inoculation then mice receiving EDIM alone or Gastrogard-R^®. Mice receiving Gastrogard-R^® however displayed an enhanced rotavirus-specific T-cell proliferation whereas rotavirus-specific antibody subtypes were not affected.

Conclusions

Preventing RRV-induced diarrhea by Gastrogard-R^® early in life showed a diminished protection against EDIM re-infection, but a rotavirus-specific immune response was developed including both B cell and T cell responses. In general, this intervention model can be used for studying clinical symptoms as well as the immune responses required for protection against viral re-infection.     

Kinetic Analysis of the Specific Host Response to a Murine Gammaherpesvirus

Respiratory infection of BALB/c mice with the murine gammaherpesvirus 68 (MHV-68) induces the clonal expansion of virus-specific cytotoxic T-lymphocyte (CTL) precursors (CTLp) in the regional, mediastinal lymph nodes (MLN). Some of these CTLps differentiate to become fully functional CTL effectors, which can be detected in both the lymphoid tissue and in the site of pathology in the lung. Though the lymph nodes and spleen harbor substantial populations of latently infected B cells for life, the level of virus-specific CTL activity decreases rapidly in all sites. The CD8⁺ CTLp numbers fall to background levels in the MLN within several months of the termination of the productive phase of MHV-68 infection in the respiratory epithelium but are maintained at relatively low frequency in the spleen. The continued presence of a gamma interferon-producing, MHV-68-specific CD4⁺ set can also be demonstrated in cultured spleen cells. The virus-specific immunoglobulin G (IgG) response is slow to develop, with serum neutralizing antibody and enzyme-linked immunosorbent assay titers continuing to rise for several months. The level of total serum IgG increases dramatically within 2 weeks of infection, probably as a consequence of polyclonal B-cell activation, and remains high. The immune response profile is clearly influenced by the persistence of this DNA virus.     

Secretory immunoglobulin A antibodies against the sigma1 outer capsid protein of reovirus type 1 Lang prevent infection of mouse Peyer's patches

Reovirus type 1 Lang (T1L) adheres to M cells in the follicle-associated epithelium of mouse intestine and exploits the transport activity of M cells to enter and infect the Peyer's patch mucosa. Adult mice that have previously cleared a reovirus T1L infection have virus-specific immunoglobulin G (IgG) in serum and IgA in secretions and are protected against reinfection. Our aim in this study was to determine whether secretory IgA is sufficient for protection of Peyer's patches against oral reovirus challenge and, if so, against which reovirus antigen(s) the IgA may be directed. Monoclonal antibodies (MAbs) of the IgA isotype, directed against the sigma1 protein of reovirus T1L, the viral adhesin, were produced and tested along with other, existing IgA and IgG MAbs against reovirus T1L outer capsid proteins. Anti-sigma1 IgA and IgG MAbs neutralized reovirus T1L in L cell plaque reduction assays and inhibited T1L adherence to L cells and Caco-2(BBe) intestinal epithelial cells in vitro, but MAbs against other proteins did not. Passive oral administration of anti-sigma1 IgA and IgG MAbs prevented Peyer's patch infection in adult mice, but other MAbs did not. When anti-sigma1 IgA and IgG MAbs were produced in mice from hybridoma backpack tumors, however, the IgA prevented Peyer's patch infection, but the IgG did not. The results provide evidence that neutralizing IgA antibodies specific for the sigma1 protein are protective in vitro and in vivo and that the presence of these antibodies in intestinal secretions is sufficient for protection against entry of reovirus T1L into Peyer's patches.     

Upregulation of ICOS on CD43+ CD4+ murine small intestinal intraepithelial lymphocytes during acute reovirus infection

Murine intestinal intraepithelial lymphocytes (IELs) can be classified according to expression of a CD43 glycoform recognized by the S7 monoclonal antibody. In this study, we examined the response of S7+ and S7- IELs in mice during acute reovirus serotype 3 (Dearing strain) infection, which was confirmed by virus-specific real-time PCR. In vivo proliferation increased significantly for both S7- and S7+ IELs on day 4 post-infection as determined by BrdU incorporation; however, expression of the inducible costimulatory (ICOS) molecule, which peaked on day 7 post-infection, was upregulated on S7+ CD4+ T cells, most of which were CD4+8- IELs. In vitro ICOS stimulation by syngeneic peritoneal macrophages induced IFN-gamma secretion from IELs from day 7 infected mice, and was suppressed by treatment with anti-ICOS mAb. Additionally, IFN-gamma mRNA increased in CD4+ IELs on day 6 post-infection. These findings indicate that S7- and S7+ IELs are differentially mobilized during the immune response to reovirus infection; that the regulated expression of ICOS is associated with S7+ IELs; and that stimulation of IELs through ICOS enhances IFN-gamma synthesis during infection.     

Rotavirus-specific protein synthesis is not necessary for recognition of infected cells by virus-specific cytotoxic T lymphocytes.

We found that rotavirus-specific protein synthesis was not necessary for recognition by virus-specific cytotoxic T lymphocytes (CTLs). In addition, CTLs lysed rotavirus-infected target cells prior to production of infectious virus. Target cell processing of rotavirus antigens for presentation to CTLs was enhanced by treatment of rotavirus with trypsin prior to infection; trypsin-induced cleavage of the viral hemagglutinin (vp4) has previously been found to facilitate rotavirus entry into target cells by direct penetration of virions through the plasma membrane. We conclude that sufficient quantities of exogenous viral proteins may be introduced into the cytoplasm for processing by target cells. The mechanism by which rotavirus proteins are processed for presentation to the target cell surface remains to be determined.     

Simian immunodeficiency virus-specific CD8+ lymphocyte response in acutely infected rhesus monkeys.

To assess the possible role of cytotoxic T lymphocytes (CTLs) in containing the spread of human immunodeficiency virus in acutely infected individuals, the temporal evolution of the virus-specific CD8+ lymphocyte response was defined in simian immunodeficiency virus of macaques (SIVmac)-infected rhesus monkeys. A brief period of SIVmac plasma antigenemia was seen 9 to 16 days following intravenous infection with SIVmac, ending as the absolute number of CD8+ peripheral blood lymphocytes (PBLs) increased. In a prospective assessment of the ability of CD8+ lymphocytes of these monkeys to suppress SIVmac replication in autologous PBLs, inhibitory activity was detected as early as 4 days, with a more pronounced effect 12 to 16 days following infection. SIVmac Gag- and Nef-specific CD8+ effector cell activities were demonstrable in PBLs of animals by 2 weeks following virus inoculation. In fact, SIVmac-specific CTL precursors were documented in the PBLs of rhesus monkeys 4 to 6 days after SIVmac infection. These studies indicate that AIDS virus-specific CD8+ CTLs are present in PBLs within days of infection and may play an important role in containing the early spread of virus.