Depletion of peritoneal CD5+ B cells has no effect on the course of Leishmania major infection in susceptible and resistant mice

Abstract

The mouse peritoneal cavity contains a unique self-renewing population of B cells (B-1) derived from fetal liver precursors and mainly producing polyreactive antibodies. Since B-1 cells are a potential source of IL-10, it has been suggested that these cells may contribute to the susceptibility of BALB/c mice to Leishmania major infection by skewing the T helper cell network towards a Th2 phenotype. Accordingly, L. major infection of B cell-defective BALB/c Xid mice (lacking B-1 cells) induces less severe disease compared with controls. However, in addition to the lack of B-1 cells, the Xid immune deficiency is characterized by high endogenous interferon-gamma (IFN-gamma) production. In the present study, the role of B-1 cells during L. major infection was investigated in mice experimentally depleted of peritoneal B-1 cells. Six weeks old C57Bl/6 and BALB/c mice were lethally irradiated and reconstituted with autologous bone marrow which allows systemic depletion of B-1 cells. Untreated BALB/c, C57Bl/6 as well as BALB/c Xid mice were used as controls. After reconstitution, mice were injected with L. major amastigotes and progression was followed using clinical, parasitological and immunological criteria. As previously reported, BALB/c Xid mice showed a significant reduction in disease progression. In contrast, despite the dramatic reduction of B-1 cells, B-1-depleted BALB/c mice showed similar or even worse disease progression compared with control BALB/c mice. No differences were found between B-1-depleted or control C57Bl/6 mice. Our data suggest that the B-1 cells do not contribute to the susceptibility of BALB/c mice to L. major infection.

Fig. 1

Lesion progression and proportion of peritoneal CD5⁺ B220⁺ B cells in BALB/c (□), C57Bl/6 (•) and BALB/c Xid mice (▴). Groups of five mice were infected in the right hind footpad with 2 × 10⁶Leishmania major amastigotes and lesion progression was monitored as described in Materials and Methods (a). The proportion of peritoneal CD5⁺ B220⁺ B cells in those groups of mice before (▪) and 9 weeks after L. major infection (□) is shown (b). Values given indicate the mean percentage and s.d.

Fig. 2

Serum-IgG anti-actin antibodies in BALB/c, C57Bl/6 or BALB/c Xid mice before (▪) and 9 weeks after Leishmania major infection (□). Sera from designated mice were diluted 1:100 and tested on the same ELISA plate. Results were expressed as a mean optical density (OD) ± s.d. that were obtained from five individual mice in each group.

Fig. 3

Course of Leishmania major infection in peritoneal B-1-depleted mice. Groups of five mice of B-1-depleted BALB/c (Δ), B-1-depleted C57Bl/6 (▪), unmanipulated BALB/c (□), and C57Bl/6 (•) mice were infected with 2 × 10⁶L. major amastigotes and the course of infection was recorded with a metric caliper (a). Footpad measurements represent the mean values (mm) ± s.d. The proportion of peritoneal CD5⁺ B220⁺ B cells in the same groups of mice was studied 9 weeks after L. major infection (□) compared with similar groups of mice without L. major infection (▪) (b). Values given indicate mean percentage ± s.d. of double-positive (B-1) cells. Parasite burden at 9 weeks of infection of the same groups of mice (c). Results are expressed as the negative of the mean of the log₁₀ dilution of footpad (▪) or draining popliteal lymph node (□) tissue positive for parasite.

Fig. 4

DTH reactivity of Leishmania major-infected mice. At 9 weeks post-infection groups of five B-1-depleted BALB/c (Δ), B-1-depleted C57Bl/6 (▪), unmanipulated BALB/c (□) and C57Bl/6 mice (•) were injected with leishmanial total antigens (LTA; 2 × 10⁶) into non-infected hind footpad. The swelling reaction (mm ± s.d.) was measured with a metric caliper at 24 h, 48 h, and 72 h.