Preliminary studies have shown a very high inhibitory activity in the alpha a and gamma zone of human serum towards the growth of Cryptococcus neoformans. These findings are now corroborated by single radial immunodiffusion tests, which showed the some loss of IgA and IgM globulins and of the other three globulin fractions (ceruloplasmin, alpha 2 macroglobulin and alpha 2 HS glycoprotein) which migrate in the alpha 2 zone. The data was obtained by single radial immunodiffusion tests. The losses were not statistically significant however. No change in the immunoglobulin content of the sera kept for 6 days in contact with a heat-killed suspension of C. neoformans was noted. These findings suggest, that the inhibitory activity of the normal human serum on the in-vitro growth of C. neoformans is due to the above mentioned globulin fractions and not to a single specific factor, Reports in literature indicate that human blood serum inhibits the growth of Cryptococcus neoformans (1,2,3).
In our own studies we have previously shown the following: (a) anticryptoccoccal activity of normal human serum is mainly found in the alpha 2 and gamma globulin fractions obtained by column electrophoresis (4), (b) the inhibitory activity was slightly reduced when the serum was heated to 56 ~ for 30 minutes and destroyed by heating to 62 ~ for 30 minutes, (c) addition of iron to a very potent * Supported by the Brown-Hazen Foundation, Susan and Bertram Brummer Foundation, and the Sigma-Xi Society. Grateful acknowledgement is given to Dr. Edward Franklin, Professor of Medicine, N.Y.U. College of Medicine, for his helpful and thoughtful criticism.