Novel role of CD8(+) T cells and major histocompatibility complex class I genes in the generation of protective CD4(+) Th1 responses during retrovirus infection in mice

Abstract

CD4(+) Th1 responses to virus infections are often necessary for the development and maintenance of virus-specific CD8(+) T-cell responses. However, in the present study with Friend murine retrovirus (FV), the reverse was also found to be true. In the absence of a responder H-2(b) allele at major histocompatibility complex (MHC) class II loci, a single H-2D(b) MHC class I allele was sufficient for the development of a CD4(+) Th1 response to FV. This effect of H-2D(b) on CD4(+) T-cell responses was dependent on CD8(+) T cells, as demonstrated by depletion studies. A direct effect of CD8(+) T-cell help in the development of CD4(+) Th1 responses to FV was also shown in vaccine studies. Vaccination of nonresponder H-2(a/a) mice induced FV-specific responses of H-2D(d)-restricted CD8(+) cytotoxic T lymphocytes (CTL). Adoptive transfer of vaccine-primed CD8(+) T cells to naive H-2(a/a) mice prior to infection resulted in the generation of FV-specific CD4(+) Th1 responses. This novel helper effect of CD8(+) T cells could be an important mechanism in the development of CD4(+) Th1 responses following vaccinations that induce CD8(+) CTL responses. The ability of MHC class I genes to facilitate CD4(+) Th1 development could also be considerable evolutionary advantage by allowing a wider variety of MHC genotypes to generate protective immune responses against intracellular pathogens.

FIG. 1.

FV-specific production of IFN-γ (A) and IL-10 (B) by purified CD4⁺ T cells. CD4⁺ T cells were purified from spleens of H-2^b/b, H-2^a/b, or H-2^a/a mice at 8 days postinfection with FV-B. The CD4⁺ T cells were cultured with irradiated syngeneic spleen cells as APCs in the presence or absence of purified UV-inactivated FV. After 72 h, culture supernatants were analyzed for cytokine production by IFN-γ- or IL-10-specific ELISA. Data shown are the average values ± standard errors of the means (SEM) for four mice per group.

FIG. 2.

Anti-IFN-γ treatment of H-2^a/b mice during infection with FV. H-2^a/b mice were given either 0.5 ml of a 0.5-mg/ml concentration of rat Ig or anti-IFN-γ (XMG1.2) every 3 days starting on the day of infection until 4 weeks postinfection with FV-B. Splenomegaly was then followed by weekly palpations of all mice. Results are given as percentages of mice that were splenomegalic or dead (8 mice per group).

FIG. 3.

Influence of MHC class I and class II genes on IFN-γ production. Purified CD4⁺ T cells from spleens of H-2^a/b, H-2^a/a, H-2^h2/a, and H-2^i18/a mice infected with FV-B were cultured with APCs and purified FV as described for Fig. 1. Data shown are the average values + SEM for four to eight mice per group.

FIG. 4.

Effect of anti-CD8 treatment of H-2^h2/a mice on IFN-γ production by CD4⁺ T cells. H-2^h2/a mice were given 0.5 ml of anti-CD8 Cellmax supernatant on days −5, −3, −1, +2, and +5 relative to the day of infection with 15 SFFU of FV-B. At 8 days postinfection, CD4⁺ T cells were purified from the spleens of infected mice and analyzed for IFN-γ production as described for Fig. 1. Data shown are the average values + SEM for eight mice per group and are the combined results of two separate experiments.

FIG. 5.

Transfer of immune CD8⁺ T cells affects IFN-γ production by CD4⁺ T cells. CD8⁺ T cells were purified by positive selection from the spleens of H-2^a/a mice at 8 days postvaccination with FV-N. More than 95% of these cells were positive for both CD8 and CD3, as analyzed by flow cytometry. Approximately 1.5 × 10⁷ CD8⁺ T cells from FV-N-vaccinated or unvaccinated H-2^a/a mice were transferred to each naive H-2^a/a mouse. As an additional control, a similar number of CD8⁻ cells were also transferred to naive H-2^a/a mice. At day 1 posttransfer, all groups were infected with 15 SFFU of FV-B. At 8 days postinfection, CD4⁺ T cells were purified and analyzed for IFN-γ production as described for Fig. 1. Data shown are the average values + SEM for four to eight mice per group and are the combined results from two separate experiments.

FIG. 6.

Anti-IFN-γ blocks CD8⁺  T-cell help. Vaccine-primed CD8⁺ T cells were purified by positive selection and transferred to naive H-2^a/a mice as described for Fig. 1. One day posttransfer, mice were infected with 15 SFFU of FV-B. Mice were then given 0.5 ml of either anti-IFN-γ Cellmax supernatant or rat Ig every other day starting on the day of infection. Alternatively, one group of H-2^a/a mice were given 10⁵ U of IFN-γ intraperitoneally on the day before infection, the day of infection, and on days 2, 4, and 6 postinfection. At 8 days postinfection, CD4⁺ T cells were purified and analyzed for IFN-γ production as described for Fig. 1. Data shown are the average values + SEM for eight mice per group and are the combined results from two separate experiments.