L. mexicana-infected cells display activation of PKCα (Figure 2b), which is confirmed by purified LPG incubated with PKCα (Figure 2a). LPG activation of PKCα then leads to enhanced oxidative burst (Figure 3a), thus reducing parasite survival, as compared with nonstimulated controls (Figure 4). It is noteworthy, that in contrast to

purified LPG, the complete parasite inhibits the respiratory burst in C57BL/6 macrophages, albeit to a lesser degree than observed for BALB/c cells. This inhibitory response in the oxidative burst induced by the whole parasite could be related to a variety of other molecules and mechanisms in addition to LPG, such as the possible recognition of opsonized parasites by CR3, a complement receptor that inhibits the oxidative burst (43). The importance of PKCα in parasite control is further strengthened by the fact that LY294002 cost the PKCα inhibitor Gö6976, which significantly reduced the oxidative burst in macrophages of both mouse strains, allowed an enhanced parasite survival in macrophages not only in BALB/c cells but also in C57BL/6 cells, which

were originally able to limit parasite survival. These data underscore the importance of the varying modulation of PKCα by L. mexicana LPG in regulating parasite survival within macrophages. R788 clinical trial The opposing response of macrophages from both mouse strains seems to be specifically related to L. mexicana LPG and not to alterations in the PKCα enzyme, as a nonspecific stimulus, such as PMA, modified the enzymatic activity of PKCα in an identical manner in macrophages of both mouse strains. The opposing effect of LPG on PKCα of both mouse strains is noteworthy, as to date, it has only been reported that L. donovani LPG inhibits ifenprodil PKC isolated from rat brain.

In that study, it was shown that LPG is a competitive inhibitor of diolein on the regulatory binding site C1 of PKC (44). Although the LPG binding site on PKCα has not been mapped, results suggest that LPG must bind to C1 region of PKC. Comparison of the primary sequence of PKCα C1 site between the two mice strains used in our study (data not shown) showed no differences between them. As post-translational modification represents a ubiquitous and essential device for control of PKC activity, localization, stability and protein–protein interaction, it would be possible that the opposite effect exhibited by LPG may be as a result of differences in post-translational modifications found in PKCα at or near this site en each mouse strain (45). In addition, it has been proposed that differences in specificities of high and low affinity phorbol ester-binding sites may partially contribute to distinct effects on PKC-regulated cellular processes (46).