TI - Discussion . AB - Human parvovirus B19-VP1u is known to have a phospholipase A2 ( PLA2 ) motif [8-12] and its enzyme activity has been associated with various inflammatory processes that may contribute to the activation of macrophages . However , little is known about the effects of B19-VP1u on macrophage activation . This is the first study to demonstrate the role of B19-VP1u and its sPLA2 enzymatic activity on the induction of macrophage responses that may contribute to inflammatory processes or diseases . Our results reveal the sPLA2 activity of recombinant B19-VP1u proteins can activate macrophages by significantly increasing migration and phagocytosis . Additionally , significant increases of MMP9 activity , IL-6 and IL-1b mRNA expression were detected in macrophages that were stimulated with B19-VP1u as well as the increased PHOSphorylation of ERK1/2 and JNK proteins . Activity of sPLA2 has been implicated in a variety of physiological and pathological responses , including cell proliferation , chemokinesis [20-22] , ECM remodeling [23-26 , 34] , vascular inflammation , [35 , 36] and cerebral ischemia [37] . Recently , parvovirus B19-VP1u has been linked with sPLA2-like activity that is recognized as group XIII enzyme [10,13] , a novel type of sPLA2 that may contribute to various pathological processes [8,26,35-38] . Additionally , a B19-VP1u mutant , B19-VP1uD175A , is mutated in the phospholipase domain and loses its enzymatic activity and viral infectivity [8-13] . However , little is known about the sPLA2 enzymatic activity of B19-VP1u in migration and phogocytosis of macrophages that is associated with a variety of inflammatory and immune responses . Notably , our experimental results reveal significant increases in migration and phagocytosis in RAW264.7 macrophage cells treated with recombinant B19-VP1u proteins as compared to the control group . In contrast , no induction of migration and phagocytosis was observed in the experimental group that was treated with B19-VP1uD175A . These experimental results strongly suggest that the sPLA2 enzymatic activity of B19-VP1u is crucial to activation of migration and phagocytosis of macrophages . Indeed , phospholipase A2 is known to play important roles in many inflammatory processes and immune responses including atherosclerosis , pro-inflammatory cytokine expression and cerebral ischemia [35 , 36] . Recent studies have demonstrated the association between extracellular-matrix-related proteins and inflammatory responses via activation of mitogen activated kinases ( MAPKs ) . In a cerebral-ischemic animal model , ischemia and organ culture were demonstrated to induce the activation of p38 , ERK 1/2 and SAPK/JNK in cerebral arteries and the expression of inflammatory and MMP9 genes in the wall of cerebral arteries [24,25,34,35,37] . Additionally , increased secretion of CXCL8 by sPLA(2) -IB is related to activation of NF-kB in human neutrophils [38] Recently , various studies have postulated MMP9 may contribute to the development or pathogenesis of autoimmunity [39] . However , the roles of B19-VP1u and its sPLA2 enzymatic activity on B19-related diseases have not been investigated . Notably , a similar phenomenon was observed in our experimental results . We demonstrated an increase in MMP-9 activity , IL-6 and IL-1beta mRNA expression and PHOSphorylation of ERK1/2 and JNK proteins in RAW264.7 cells that were treated with recombinant B19-VP1u proteins . In contrast , no inductive effects on inflammatory related responses were observed in RAW264.7 cells treated with mutant B19-VP1uD175A protein or B19-VP1u with inhibitors . These experimental results strongly indicate the importance of sPLA2 activity of B19-VP1u in activation of macrophages and suggest the involvement of B19-VP1u and its PLA2 activity in inflammatory processes via activation of ERK1/2 and JNK signaling pathways in macrophages .