Various antigenic reactivities in delayed hypersensitivity among crystalline proteins from Mycobacterium phlei

Comparisons were made of the delayed-type skin reactivity of 6 crystalline proteins purified from the cell extract of Mycobacterium phlei in guinea pigs sensitized with whole cells of the heat-killed bacillus. These highly purified proteins elicited varying degrees of cutaneous reaction. The most active protein had almost the same reactivity as purified protein derivative prepared from the culture filtrate of Mycobacterium phlei. On the other hand, the weakest protein did not elicit a marked cutaneous reaction even after injection of 3,000 times the amount of protein of the most potent one. The other 4 proteins showed moderate reactivities. The difference in antigenic potency between proteins is probably due not to the amounts of the proteins contained in the cells used for sensitization, but to their structure.