immunology of infectious and parasitic diseases - XXXVII Congress ...

PI3K CONFERS RESISTENCE AGAINST Trypanosoma cruzi INFECTION
DUE TO ITS IMPORTANT ROLE IN LYMPHOCYTE PROLIFERATION AND
MICROBICIDAL ACTIVITY OF MACROPHAGES
MARIA CLÁUDIA DA SILVA (1) ; RENATA SESTI (1) ; FABRÍCIO C. DIAS (1) ;
GRACE K. SILVA (1) ; TIAGO DA SILVA MEDINA (1) ; FERNANDO Q. CUNHA (1) ;
JOÃO SANTANA DA SILVA (1) ; THIAGO MATTAR CUNHA (1)
(1) School of Medicine of Ribeirão Preto, University of São Paulo (USP),
Ribeirão Preto, São Paulo - Brazil.
Background and objective: The phosphatidylinositol-3-kinases (PI3Ks) are a
family of lipid kinases that plays a crucial role in several cellular processes
including survival and proliferation. Among PI3Ks, PI3K is a member activated
by G protein coupled receptors, involved in the signaling of chemotactic factors
and leukocytes migration and activation. In this study, we evaluated the role of
PI3K during experimental infection by T. cruzi. Methods: C57BL/6 WT and
PI3K -/- mice were infected with 10 3 forms of T. cruzi Y strain. Ten days after
infection, the heart tissue was harvested for quantification of PI3K activation.
For evaluation of PI3K role eighteen days after T. cruzi infection, heart tissue
was harvested for assessment of inflammation, lesion and parasitism, and we
observed daily the parasitemia and survival rate of WT and PI3K -/- mice. The
involvement of PI3K in the killing of the parasite and NO production was
assessed in bone marrow-derived macrophages from WT and PI3K -/- mice. To
verify whether PI3K signaling influenced the in vitro T cell proliferation,
splenocytes stained with CFSE from both groups were stimulated with ConA
and α-CD3 during 72 hours. Results: T. cruzi infection causes an increase in
the PI3K activation in the heart tissue. Although there is no difference in the
parasitemia between WT and PI3K -/- mice in all times evaluated, all PI3K
deficient mice died until day 25 after infection, whereas WT mice remained alive
after 35 days. PI3K -/- mice also showed greater inflammation, parasitism and
lesion in the heart tissue. Interestingly, in the absence of PI3K, the heart tissue
express five times higher levels of iNOS enzyme after infection compared with
WT mice, but the expression of arginase I (ARG1), that also consume the
amino acid arginine thus impairing the NO production, is twenty times higher
compared with WT mice. In vitro, macrophages from PI3K -/- mice, when
stimulated with IFN, fail to produce NO and to kill the parasite. Corroborating
these data, the addition of ARG1 inhibitor reverts the fail in NO production by
PI3K -/- macrophages. Finally, PI3K signaling seems to be involved in the
adaptive response, augmenting T cell proliferation. Conclusion: These results
indicate that PI3K is critical for the host to control T. cruzi parasitism. In the
heart tissue of the infected mice, PI3K is involved in the microbicidal
mechanisms of macrophage by mediation of NO production.