Identification and characterization of autoantibody-producing B220low B (B-1) cells appearing in malarial infection

Mice with malaria showed unique immunological responses, including the expansion of NK1.1−TCRint cells (extrathymic T cells). Since TCRint cells with autoreactivity and autoantibody-producing B cells (B-1 cells) are often simultaneously activated under autoimmune conditions, it was examined whether B-1 cells were activated in the course of malarial infection. From days 14 after infection, B220low B-1 cells appeared in the liver and spleen. The number of B220low B cells was highest at day 14, but the ratio was highest at days 28–35. In parallel with the appearance of B220low cells, autoantibodies against HEp-2 cells and double-stranded DNA were detected in sera. These B220low cells had phenotypes of CD44high, CD23− and CD62L−. In sharp contrast, conventional B220high B cells (B-2 cells) were CD44low, CD23+ and CD62L+. These results suggested that malaria immune responses were not mediated by conventional T and B cells but resembled the responses during autoimmune diseases.