Influence of the genetic background and parasite load of mice on the immune response developed against nymphs of Ixodes ricinus

The immune response of BALB/c (H-2d), DBA (H-2d), C57BL/6 (H-2b), C3H (H-2k ), CBA (H-2k), SJL (H-2s), and FVB (H-2q) mice infested once with 15 nymphs of Ixodes ricinus is polarized toward Th2 as suggested by cytokines produc ed by lymph node cells stimulated with concanavalin A. The parasite load do es not influence the polarization of the immune response as observed in BAL B/c mice, which developed a Th2 response when infested with 5 or 45 nymphs. As assessed by attachment and weights of engorged nymphs, no resistance wa s acquired by BALB/c, C57BL/6, or C3H mice undergoing three successive infe stations. However, these mice produced a gradual increase in IgE.