The Loss and Gain of Marginal Zone and Peritoneal B Cells Is Different in Response to Relapsing Fever and Lyme Disease Borrelia

T cell-independent Abs are protective against Lyme disease and relapsing fever, illnesses caused by Borrelia spirochetes with distinct blood-borne phases of infection. To understand this protective response, we characterized splenic and peritoneal B cell compartments during infection using flow cytometry and immunohistochemistry. In the spleen, early after infection, Borrelia crocidurae, a relapsing fever species, induced a striking loss of marginal zone (MZ) B cells from the MZ, while Borrelia burgdorferi, the agent of Lyme disease, induced the expansion of this subset. At the same time, no significant changes were observed in follicular B cells in response to either species of Borrelia. In the peritoneal cavity, a further loss was demonstrated early in response to B. crocidurae in the B1b, B1c, and B2 cell subsets, but B1a cells were not significantly altered. The loss of B1c and B2 cells was sustained through subsequent peaks of spirochetemia, suggesting these subsets may be important in resolving relapsing episodes. In contrast, an early and significant increase in peritoneal B1a, B1b, and B1c cells, but not B2 cells, occurred in response to B. burgdorferi. Later in the course of infection, both species of Borrelia induced the selective expansion of peritoneal B1b cells, suggesting that B1b cells may participate in long-lasting immunity to Lyme and relapsing fever spirochetes. Our data demonstrate that different Borrelia can activate the same B cell subsets in distinct ways and they each elicit a complex interplay of MZ and multiple peritoneal B cell subsets in the early response to infection.