Circulating immune complexes and in vitro cell reactivity in paracoccidioidomycosis

The severest forms of paracoccidioidomycosis (Pcm) are associated with impaired cell-mediated immunity, a phenomenon that is reversible with therapy. It has been postulated that plasma factors could be responsible for such immune dysfunction. In this report, circulating immune complexes (CIC) were measured by the Raji cell radioimmunoassay (Raji) and by the¹²⁵I-C1q binding assay (C1q-BA) in sera from 14 patients with either active or inactive forms of Pcm and from 15 healthy controls. The C1q-B A revealed significantly elevated levels of CIC in the sera of all but one of the patients. Four of the 8 active (62%) and 2 of the 6 inactive (33%) patients had CIC levels significantly higher than the controls as determined by the Raji test. Significantly increased levels of CIC were detected only in the active patients by the Raji test. The serum of one of the patients, with a generalized infection and depressed lymphocyte responsiveness, was examined and found to contain a factor which depressed the in vitro proliferation of both homologous and normal lymphocytes. We also found that pre-culture of the patients' lymphocytes before stimulation restored their proliferative capacity, and IC were detectable in the culture supernatants. However, the subsequent addition of the patients' serum to such precultured cells did not reinduce the depression. It is suggested therefore, that the depression of T cell responses observed in Pcm is due to the presence of IC which may interact reversibly with the responding cells and/or activate a suppressor cell population whose activity is diminished by preculture.