A mannoprotein constituent of Candida albicans cooperates with antigen in the induction of a specific primary antibody response in cultures of human lymphocytes.

The effects of Candida albicans mannoproteins on the induction of a primary antibody response to a T-dependent antigen, sheep erythrocytes (SRBC), in cultures of human blood lymphocytes, were investigated. Two experimental systems (bulk and limiting dilution cultures) allowing the detection of both enhancing and inhibitory effects, were used. In bulk cultures, antigen alone elicited a small number of specific antibody forming cells, unless IL-2 was supplied. Addition of the fungal mannoprotein extract or of a purified constituent of it increased 5 to more than 10 times the specific response. When limiting dilution analysis was performed, we observed that: a) a similar number of specific precursor cells was induced by antigen and either IL-2 or mannoprotein; b) the plot of the number of seeded cells versus the log of the fraction of negative cultures was linear in antigen and IL-2 triggered cultures but constantly deviated from linearity when the candidal stimulant was added. Thus, more than one type of precursor cell was limiting in these cultures, and the immunoenhancing effect of mannoprotein may involve multiple cellular interactions.