Most tetramer+ SIV-specific CD8 T cells expressed perforin during early SIV infection.

(A) Representative lymph node section stained with Mamu-A*001:01/Gag CM9 tetramers (red) and perforin (green) showing perforin negative, perforin low, perforin medium and perforin high MHC-class I tetramer+ SIV-specific CD8 T cells. Scale bar indicates 10 μm. (B) Percentages of tetramer+ SIV-specific CD8 T cells that expressed perforin in follicular and extrafollicular regions. Among tetramer+ SIV-specific CD8 T cells, the distribution of cells across perforin negative, low, medium and high was not significantly different between follicular and extrafollicular regions. A significantly higher percentage of tetramer+ SIV-specific CD8 T cells during early SIV infection expressed perforin than those during chronic SIV infection in both (C) follicular areas (p = 0.0205), and (D) extrafollicular area (p = 0.0205). Simultaneously, the percentages of tetramer+ SIV-specific CD8 T cells during early SIV infection tended to express a higher level of perforin than those during chronic SIV infection in (E) follicular regions (p = 0.0536), and (F) were statistically significant in extrafollicular regions (p = 0.0364).