Antigen-mediated fusion of specifically sensitized rabbit alveolar macrophages.

Rabbits sensitized intravenously with heat-killed Mycobacterium tuberculosis (strain H37Ra) suspended in mineral oil developed a strong pulmonary granulomatous response which reached its peak about 3 to 4 weeks after injection. Alveolar cells (4 x 10(6) cells/ml of tissue culture medium 199) procured 6 weeks after sensitization showed extensive development of multinucleated giant cells after 12 hr of incubation in tissue culture flasks containing heat-killed H37Ra (5 mug/ml). Giant cells measured 80 mum to 2.5 mm in length and contained between 30 and 700 nuclei. In contrast, no giant cells were observed when similar samples of the same cell populations were incubated in flasks containing: (i) no mycobacteria; (ii) heat-killed Escherichia coli; (iii) heat-killed Bacillus subtilis; (iv) latex particles; (v) ovalbumin; or (vi) phytohemagglutinin. The addition of immune (anti-H37Ra) sera potentiated the phenomenon of giant cell formation. In addition, supernatant fluids obtained from sensitive alveolar cells incubated with H37Ra were capable of inducing giant cell formation when incubated with nonsensitized alveolar cells. The results suggest that fusion of alveolar macrophages is mediated by an immunological mechanism.