Pancreatic lipase-related protein 2 (
PLRP2) is induced by
IL-4 in vitro in cytotoxic T lymphocyte (CTL) clones and CTLs from immunized wild-type (WT)
PLRP2(+/+) are more cytotoxic than
PLRP2(-/-) CTLs, suggesting to previous investigators that the
lipase PLRP2 might support CTL functions. Here, we further evaluate
PLRP2 in CTLs. We found that
PLRP2 was optimally induced in splenocytes by 3.5 x 10(-8) M
IL-4 by day 6 after activation and was restricted to CD8(+) T cells.
PLRP2 mRNA was detected inconsistently (and at low levels) after activation in the presence of
IL-2. Cytotoxicity in 4 h (51)Cr assays of WT CTLs was approximately 3-fold the activity of
PLRP2(-/-) CTLs cultured with
IL-4 and, with
IL-2, was unexpectedly approximately 2 fold the activity of
PLRP2(-/-) CTLs. Thus,
PLRP2 gene ablation affected short-term (
perforin-dependent) cytotoxicity, even under the
IL-2 conditions. Other variables failed to account for the reduced cytotoxicity.
Granzyme B levels, activation markers, and CD8(+) T cell frequencies were similar for WT vs.
PLRP2(-/-) CTLs (with either
cytokine). Addition of rPLRP2 to
IL-4 induced
PLRP2(-/-) CTLs (or to cytotoxic granule extracts) failed to increase lysis, suggesting that the missing mediator is more than released
PLRP2. Cytotoxicity of WT and
PLRP2(-/-) CTLs was similar in 2-day
tumor survival assays with
IL-4, which can be mediated by
perforin-independent mechanisms. We conclude that extracellular
PLRP2 lipase is unable to directly augment the cytotoxicity that was lost by
PLRP2 ablation and that after reevaluation, the question of what is
PLRP2's role in CD8 T cells is still unanswered.