Spontaneous and pokeweed mitogen-induced in vitro IgG production specific for S. aureus cell wall determinants in man

A system has been established to produce in vitro IgG specific for cell wall determinants of S. aureus by human peripheral blood mononuclear cells (PBMC). PBMC of healthy individuals, of patients with S. aureus infections and of patients with other bacterial infections were cultured for 12 days. In the culture supernatants (SN) total IgG was determined by a competitive RIA, and IgG to purified cell walls (PCW) of S. aureus strain H by a two step ELISA. PBMC of 11 healthy persons produced anti-PCW IgG upon stimulation by pokeweed mitogen (PWM). This indicates the presence in some healthy persons of circulating B cells which can be induced in vitro to synthesize PCW specific IgG. PBMC of S. aureus infected patients, however, synthesized anti-PCW IgG in culture medium alone. This is the first description of spontaneous in vitro production of specific IgG during a bacterial infection and may be analogous to short phases of spontaneous specific IgG production described after immunizations and viral infections. Finally, compared to healthy individuals, an increased total IgG synthesis in vitro by PBMC obtained from patients with S. aureus and from patients with other severe bacterial infections was found. It is concluded that this polyclonal B cell activation has been initiated in vivo. Its biological significance is unknown.