Serum-mediated immune cellular responses to Brucella melitensis. IV. Infection of macrophages under anaerobic conditions.

Immune mechanisms active against Brucella were studied under conditions of oxygen deficiency. B. melitensis grew in rabbit serum-Tyrode medium flooded with N(2) and CO(2) gas mixtures. Immune sera from rabbits injected with B. melitensis strain Rev I possessed growth-inhibitory activity that operated in anaerobic environments against Rev I and virulent strain 6015. When mixed with macrophages, immune sera mediated even greater inhibition of bacterial growth and slowed the spread of infection throughout the tissue culture. Although under anaerobic conditions the rate of phagocytosis was reduced, the macrophages in immune serum killed significant percentages of Brucella, suggesting that an antibacterial mechanism had been activated. Sonic extracts of macrophages prepared and tested under anaerobic conditions depressed the growth rate of strain Rev I. The extracts, however, exhibited no immediate killing capacity when tested in Tyrode solution. A factor from serum was required for depression of the growth rate.