Private specificities of CD8 T cell responses control patterns of heterologous immunity

Abstract

CD8 T cell cross-reactivity between viruses can play roles in protective heterologous immunity and damaging immunopathology. This cross-reactivity is sometimes predictable, such as between lymphocytic choriomeningitis virus (LCMV) and Pichinde virus, where cross-reactive epitopes share six out of eight amino acids. Here, however, we demonstrate more subtle and less predictable cross-reactivity between LCMV and the unrelated vaccinia virus (VV). Epitope-specific T cell receptor usage differed between individual LCMV-infected C57BL/6 mice, even though the mice had similar epitope-specific T cell hierarchies. LCMV-immune mice challenged with VV showed variations, albeit in a distinct hierarchy, in proliferative expansions of and down-regulation of IL-7Ralpha by T cells specific to different LCMV epitopes. T cell responses to a VV-encoded epitope that is cross-reactive with LCMV fluctuated greatly in VV-infected LCMV-immune mice. Adoptive transfers of splenocytes from individual LCMV-immune donors resulted in nearly identical VV-induced responses in each of several recipients, but responses differed depending on the donor. This indicates that the specificities of T cell responses that are not shared between individuals may influence cross-reactivity with other antigens and play roles in heterologous immunity upon encounter with another pathogen. This variability in cross-reactive T cell expansion that is unique to the individual may underlie variation in the pathogenesis of infectious diseases.

Figure 1.

Longitudinal analysis of LCMV-specific memory CD8 T cells on heterologous PV or VV infection. The frequency and the hierarchy of LCMV-specific CD8 T cells in the peripheral blood of individual LCMV-immune mice were examined via IFN-γ assay before (day 0) (A) PV or (B) VV infection and after the heterologous viral challenge (day 12). Plots show the LCMV epitope–induced IFN-γ production from gated CD8 T cells costained with the activation/memory marker CD44 for better resolution. The percentages of epitope-specific CD8 T cells before and after virus infections were determined (top right quadrants) and the percent changes in those values are shown. The epitope-specific CD8 T cell percentages with a >1.5-fold increase are indicated with a bold outline box. Representative figures are shown for 3 out of 10 PV-infected and out of 26 VV- infected LCMV-immune mice (Table I). (C) Alterations in the LCMV-specific CD8 T cell repertoire in the individual VV-infected LCMV-immune mice. The relative proportion of LCMV epitope–specific CD8 T cells (total percentage being 100%) in the individual LCMV-immune mice was compared before (white bar) and after (black bar) VV infections. *, epitope-specific CD8 T cells showing a >50% increase in their relative proportion upon VV infection. Representative data are shown for 6 out of 26 VV-infected LCMV-immune mice. (D) Time course of VV-induced LCMV-specific epitope response. Individual LCMV-immune mice were sequentially bled before and at days 4, 7, and 12 after VV challenge. This figure, showing a preferential response to NP205, is representative of similar experiments performed on 10 mice.

Figure 2.

Selective down-regulation of IL-7Rα on LCMV-specific memory CD8 T cells on LCMV or VV infection. The levels of IL-7Rα expression on LCMV epitope–specific memory CD8 T cells, visualized via IFN-γ assay, were examined in LCMV-immune mice or LCMV-immune mice infected with homologous high dose (5 × 10⁶ PFU) clone 13 strain of LCMV or heterologous VV 6 d after infection. The percentages above the top left quadrant of dot plots represent the proportion of the IL-7Rα^low subset out of the total epitope-specific CD8 T cells. Outlined boxes indicate the epitope-specific CD8 T cells, in which >20% of the subset show down-regulation of IL-7Rα. Representative data are shown for 3 out of 10 VV-infected LCMV-immune mice.

Figure 3.

LCMV-immune CD8 T cells from a single donor exhibit remarkably similar VV-induced responses among several recipient hosts. (A) CFSE-labeled LCMV-immune donor cells derived from a single donor were transferred into multiple hosts, which were infected with VV. (B) Donor-derived LCMV epitope–specific CD8 T cells were visualized in multiple recipient mice infected with VV (day 6). Two representative experiments are shown out of 17 individual donor-recipients pairs (Table II).

Figure 4.

Variations in response to a VV-encoded epitope cross- reactive with LCMV-specific T cells. (A) MHC tetramer staining of cells from an A11R 198-stimulated T cell culture derived from an LCMV-immune mouse. Sample is costained with K^b tetramers charged with either the A11R198 or the GP118 peptide. (B) The frequencies of VV-derived A11R 198 epitope-specific CD8 T cells were followed via IFN-γ assay in the peripheral blood of individual LCMV-immune mice before (D0) and after (D12) VV infection. Representative data are shown for 9 out of 19 VV- infected LCMV-immune mice. (C) Adoptive transfer experiments showing private specificities of A11R 198 responses. Splenocytes from LCMV- immune mice were labeled with CFSE and transferred from one donor into two recipients. A11R 198- and GP276-specific responses were monitored 6 d later, as in Fig. 3 B.