Amounts of trehalose-6,6-dimycolate as small as 1 to 5 ,ug can, after intravenous injection, induce in the lungs of mice formation of tubercles in which the cellular composition is indistinguishable from that in tubercles formed after an infection with living BCG bacilli. The strongest cellular response in mice was induced by cord factor from Mycobacteriwn kansasii; the weakest was induced by cord factor from the BCG strain of M. bovis. It was found that three intravenous injections of cord factor induced a more extensive cellular response than did one injection of the same total amount of cord factor. Mice treated intravenously with cord factor were protected against an intravenous challenge with the virulent H37Rv strain of M. tuberculosis. The cellular response in the lungs of mice to intraperitoneal injections of living BCG and cord factor was very weak compared with that after intravenous injections. Intraperitoneal vaccination of mice with cord factor did not protect the mice against a challenge with virulent tubercle bacilli. Mice vaccinated intraperitoneally with BCG were immunized although no granulomas, or very few, were present in the lungs at the time of the challenge. The significance of the cellular response induced by cord factor is discussed.

Trehalose-6,6-dimycolate (cord factor), a glycolipid from mycobacteria, suppressed the development of urethan-induced tumors in the lungs of mice to a similar degree as living Mycobacterium bovis (strain BCG) bacilli. The inhibition was apparently due to the host cellular reaction caused locally by cord factor.

Injection of emulsified 6,6'-di-O-2-tetradecyl-3-hydroxyoctadecanoyl-a, a trehalose designated C76, a synthetic analogue of the mycobacterial glycolipid trehalose-6,6'-dimycolate (TDM), into transplants of an established, syngeneic murine fibrosarcoma induced complete regression of tumor in a number of animals. The number of animals in which tumor regressed completely dependent on the amount of oil in the emulsion. On a weight basis, C76 was at least as active as TDM. Intralesional injection of an emulsified mixture of C76 and endotoxin (ET) or of TDM and ET caused regression of an established transplant of a guinea-pig hepatoma in syngeneic animals. In mice, intravenously administered emulsions of C76 were less toxic and less granulomagenic than those made with TDM.

Ten micrograms of trehalose-6,6'-dimycolate (cord factor) injected into the footpads of mice increased the antibody response to sheep red blood cells (SRBC) subsequently injected into the same sites. There is a relationship between the antibody response and the cellular reaction induced locally and in the draining lymph nodes by cord factor, as judged by a much weaker response when antigen is injected into the contralateral footpads. The time intervals between injection of cord factor and antigen were from 5 to 20 days. A similar increased antibody response to SRBC was evident after preliminary administration of Freund's complete adjuvant or living BCG bacilli into the footpads. There was no increased antibody response in mice pretreated with living BCG or Freund's adjuvant to SRBC injected into the contralateral footpads. Administration of wax D from human strains Peurois and Test was without any effect. Administration of SRBC emulsified in incomplete Freund's adjuvant containing 5 ,ug of cord factor induced a very strong antibody response in the mice as compared to that after injection of the same amount of antigen in incomplete Freund's adjuvant containing wax D or mycobacteria. The results are discussed.