Expression of cytoplasmic granules with T cell‐associated serine proteinase‐1 activity in Ly‐2(CD8) T lymphocytes responding to lymphocytic choriomeningitis virus in vivo

Monoclonal antibodies (mAb) with specificity for the T cell‐associated serine proteinase‐1 of the mouse (MTSP‐1) were used to study expression and storage of this enzyme in T lymphocytes during lymphocytic choriomeningitis (LCM) virus infection in vivo. Immunohistochemical analysis of splenic tissue at the peak of LCM virus‐specific T cell‐mediated cytolytic responses, i.e., at day 7 post infection, revealed high numbers of MTSP‐1 T lymphocytes in the interfollicular T cell‐dependent area of the spleen. More than 50% of Ly‐2(CD8) cells but only low numbers of Ly‐2^‐(CD8^‐) cells, previously enriched by flow cytofluorometry, contained large amounts of cytoplasmic granules which stained both with MTSP‐1‐specific mAb and the esterase substrate N‐α‐benzyloxycarbonyl‐L‐lysine thiobenzyl ester. These data demonstrate that in vivo generated LCM virus‐induced cytolytic T lymphocytes develop cytoplasmic storage granules containing MTSP‐1 and suggest that the mechanism of granule exocytosis is operative in vivo; possibly MTSP‐1 is one effector molecule participating in the Ly‐2(CD8) T lymphocyte‐mediated control of virus infection.