BALB C MICE INFECTED WITH BRUCELLA-ABORTUS EXPRESS PROTRACTED POLYCLONAL RESPONSES OF BOTH IGG2A AND IGG3 ISOTYPES/

A polyclonal IgG2a response dependent on the secretion of endogenous I FN-gamma has been demonstrated in BALB/c mice injected with killed who le cells of Brucella abortus [1]. Here we report intense and protracte d polyclonal responses of IgG2a and also of IgG3 isotypes in BALB/c mi ce undergoing primary infections with B. abortus attenuated vaccine st rain 19 or virulent strain 2308. Ratios of total serum Ig levels betwe en infected mice and age matched controls were greater than 38 for IgG 3 and greater than 12 for IgG2a between weeks 4 and 8 post-infection. Polyclonal increases of IgM and IgG1 that were proportionally much low er (ratios <2 and less than or equal to 3, respectively) also occurred in infected mice during this time. It is hypothesized that both IgG3 and IgG2a polyclonal responses required IFN-gamma, which was induced b y B. abortus primarily in a T cell-independent fashion during the firs t weeks of infection, and from T cells thereafter.