Modulation of the IgG subclass responses to lipopolysaccharide by bacterial membrane components: differential adjuvant effects produced by primary and secondary stimulation.

The characteristic modulating effects of bacterial membrane adjuvants on the IgG subclass responses to lipopolysaccharide (LPS) were further investigated. Previous studies indicated that more hydrophobic adjuvants preferentially augmented the number of LPS-specific IgG1 plaque-forming cells (PFC) whereas more hydrophilic adjuvants induced predominantly IgG2 PFC, and that complex formation between LPS and adjuvants was necessary for this modulation. In the present report, no carrier effect of adjuvants in the classic immunologic sense could be detected. Undiminished secondary IgG responses to LPS were obtained regardless of which adjuvant was used for the secondary injection. When IgG subclass responses were examined, however, differential effects of adjuvants produced by primary and secondary injections were observed. The adjuvant used in combination with LPS for the primary stimulus determined the number and subclass of LPS-specific IgG memory cells induced: The same or a different adjuvant used with LPS for the secondary stimulus effected the induction of these memory cells to antibody-producing cells. The pattern set by the primary stimulus was not altered by the secondary stimulus, regardless of the potential modulating effect of the second adjuvant.