Immunogenicity of lysozyme derivatives lipid-conjugated to various degrees in mice treated with and without cyclophosphamide: dissociation of delayed-type hypersensitivity and helper function.

Lysozyme and a series of its lipid-conjugated derivatives without adjuvant were examined in mice for their abilities to induce delayed-type hypersensitivity (DTH), helper T-cell activity, and antibody formation. In addition, the effect of cyclophosphamide (CY) on the immune responses was assessed in mice immunized with these lysozyme derivatives. Precipitated lysozyme without lipid conjugation was a good inducer of both antibody and DTH responses. Lipid conjugation to lysozyme to intermediate degrees readily caused the failure only in inducing the antibody response. As lysozyme was lipid-conjugated more heavily, DTH response was also reduced and finally abolished. In contrast, the helper activity was little affected by any degree of lipid conjugation. These results indicate that the helper T-cell activity was dissociated from the both DTH response and the antibody production. CY pretreatment extensively enhanced DTH response induced by such lipid-conjugated derivatives that failed to induce antibody response. Furthermore, CY pretreatment in doses in a wide range enhanced not only DTH response but also antibody formation. It is, therefore, concluded that the enhancement of DTH response by CY does not necessarily entail suppression of antibody formation.