We tested the effect of 33 ergot alkaloids (natural and semisynthetic) on the induction of antibody formation in isolated spleen cells by antigen in tissue cultures. The results are quantitatively expressed as the number of antibody-forming cells. The group of natural ergot alkaloids (ergopeptines) exerted an effective inhibitory action on the antibody response. Compounds derived from lysergic acid are completely inactive in this respect. A new, very active semisynthetic drug (Table 1, compounds 2) derived from inactive lysergol was described. The compounds interacting with alpha-adrenergic-receptors on lymphocytes (methoxamine, phentolamine, prazosin act synergistically with the inhibitory effect of ergopeptine alkaloids.

Institute of Microbiology Czechoslovak Academy of Sciences Prague

Immunomodulators isolated from microorganisms