TLRs innate immunereceptors and Plasmodium falciparum erythrocyte membrane protein 1 (PfEMP1) CIDR1α-driven human polyclonal B-cell activation

Chronic malaria severely affects the immune system and causes polyclonal B-cell activation, as evidenced by the presence of hypergammaglobulinemia, elevated levels of autoantibodies, loss of B-cell memory and the frequent occurrence of Burkitt's lymphomas (BL) in children living in malaria endemic areas. Previous studies have shown that the cysteine-rich interdomain region 1 alpha (CIDR1 alpha) of the Plasmodium falciparum erythrocyte membrane protein 1 (PfEMP1) of the FCR3S1.2 strain, subsequently named CIDR1a, interacts with B cells partially through the binding to the B-cell receptor (BCR). This interaction leads to an activated phenotype, increased survival, and a low degree of proliferation. CIDR1 alpha preferentially activates the memory B-cell compartment, therefore PfEMP1 is considered to act as a polyclonal B-cell activator and its role in memory maintenance has been suggested. In this report, we extend the analysis of the PfEMP1-CIDR1 alpha B-cell interaction and demonstrate that PfEMP1-CIDR1 alpha increases the expression of TLR7 and TLR10 mRNA transcripts and sensitizes B cells to TLR9 signalling via the MyD88 adaptor molecule. Furthermore, despite its ability to bind to surface Igs, PfEMP1-CIDR1 alpha-induced B-cell activation does not seem to proceed through the BCR, since it does not induce Lyn and/or phospho-tyrosine mediated signalling pathways. Rather PfEMP1-CIDR1 alpha induces the phosphorylation of downstream kinases, such as ERK1/2, p38 and IKB alpha, in human B cells. These findings indicate that PfEMP1-CIDR1 alpha induces a persistent activation of B cells, which in turn can contribute to the exhaustion and impairment of B-cell functions during chronic malaria infection. (C) 2011 Elsevier B.V. All rights reserved.