CD36: Hemin interaction axis to control immune responses and cytokine secretion from macrophages involving Lyn kinase.

Abstract

The intensity and duration of TNF- production are mutually correlated with the level of CD36 expression level. The macrophages exposed to hemin exhibits modulation of non-opsonic phagocytosis of aged RBCs and ability to kill bacteria. Immuno-fluorescence study indicates translocation and sequestration of CD36 within the intracellular storage in the hemin treated macrophages. It in-tern dysregulate the global cytokine secretion from macrophages. CD36 has suitable hemin biophoric environment involving R292, D372 and Q382 to bind and the mutation in biophore residues (R292A, D372A or Q382A) significantly reduced the affinity. Ectopic expression of CD36 in MG63 cells showed several folds increment in cytokines TNF-, MCP-1, RANTES and CCL1 in response to hemin stimulation but no significant amount of cytokines released with mutants (R292A, D372A or Q382A), highlights the relevance of CD36-hemin interaction for immune-dysfunction. Hemin is driving down-stream signalling involving CD36 and subsequent recruitment of adaptor proteins to the cytosolic domain of CD36. Immuno-precipitation of membrane bound CD36 and detection of adaptor proteins indicate change in level of Lyn proteins with CD36 fractions after hemin stimulation to macrophages. The Lyn targeted siRNA restored the phagocytic activity, reduced the secretion of pro-inflammatory cytokine levels clearly suggests the Src family protein Lyn is crucial for CD36-hemin mediated immune dysregulation and cytokine secretion. In summary, hemin-CD36-Lyn cytokine signalling axis could be a contribution factor to severe malaria pathology and prognosis.