Mannan as an antigen in cell-mediated immunity (CMI) assays and as a modulator of mannan-specific CMI

Mannan (MAN) extracted from Candida albicans 20A was investigated for its potential as an antigen in the detection of cell-mediated immunity (CMI) in vivo and in vitro and for its ability to modulate CMI when administered intravenously (i.v.). CBA/J mice were either immunized as adults by the cutaneous inoculation of 10(6) viable blastoconidia or colonized as infants (primed) and then boosted cutaneously as adults. When immunized animals were footpad tested with MAN, highly significant delayed-type hypersensitivity (DH) responses were detected. The DH responses to MAN were of a greater magnitude than those noted with the same quantity of cell wall glycoprotein (GP), an ethylenediamine extract of the cell wall which contains both glucan and MAN. In contrast, GP was a better antigen for the detection of CMI responses in an in vitro lymphoproliferative assay with either spleen or lymph node cell suspensions. Mice treated with MAN i.v. prior to the initiation of immunization or between priming and secondary inoculations developed significantly suppressed DH reactions when tested with either MAN or GP. The lowest effective dose of MAN was 250 micrograms, maximum suppression occurred with 500 micrograms, and either dose given 1 week prior to immunization was suppressive. The suppression by MAN was specific for MAN or the MAN-containing GP. Responses to another unrelated candidal antigen, a membrane extract designated BEX, were relatively unaffected. MAN, therefore, was an effective antigen for the detection of CMI in vivo, and its administration i.v. created what appeared to be a MAN-specific suppression since it could be detected with both MAN and a MAN-containing extract from the cell wall. Caution must be exercised in the interpretation of these data, however, since the protein component of each of these extracts has not been characterized with respect to its potential role in the phenomena observed.