Phagocytosis and killing of Brucella by human polymorphonuclear leukocytes.

Although cellular immunity involving activated macrophages is important in resistance to Brucella, serum factors and polymorphonuclear leukocytes (PMNLs) play some role in the initial response to infection. The interaction between human PMNLs and virulent and attenuated strains of Brucella abortus and Brucella melitensis was studied by in vitro techniques. Virulent and attenuated strains of both species were rapidly phagocytosed after opsonization with normal human serum (NHS); nonopsonized bacteria were not phagocytosed. In contrast, NHS devoid of detectable antibodies was bactericidal for strains of B. abortus but not of B. melitensis. In addition, intracellular killing of ingested bacteria was shown for virulent B. abortus but not for B. melitensis. Ultrastructural studies revealed morphological alterations in about one-half of phagocytosed B. abortus and B. melitensis after incubation for 10 min; thereafter, nearly 100% of B. abortus showed some degree of degeneration, whereas B. melitensis remained intact during 120 min of observation.