Experimental production of pulmonary granulomas; II. Age dependency and immune modulation of granuloma production

Endobronchial instillation of Freund's complete adjuvant (FCA) induced epithelioid cell granulomas in the lungs of juvenile rabbits which had been kept free from contamination with the microbiol antigens. The granulomas were named "juvenile granulomas", because, unlike FCA granulomas in adult animals, prior immunization was unnecessary for their induction. The granulomas developed in several weeks with a peak at 14 weeks of age, after which the production decreased gradually. The rate of granuloma production seemed to vary with the acquisition of skin hypersensitivity to tuberculin (OT), suggesting that granuloma production, as well as skin hypersensitivity, is in the category of T-dependent immune reactions. In fact, T-generating lymphoid organs developed in parallel with the dermal and pulmonary reactions. Thus, juvenile rabbits at about 14 weeks of age are most susceptible to the microbial antigens. This susceptibility results in the unexpected production of immune granulomas in response to depot antigens at the site of instillation. The treatment of foetal or neonatal rabbits with FCA markedly suppressed granuloma production in juveniles but not in adults and did suppress but gradually enhanced the tuberculin skin reaction. It is suggested that generation of suppressor T cells is the cause of suppression of juvenile granuloma production.