Observations on the antigenic differences between the so-called SC and LC strains of Mycoplasma mycoides subsp....

The so-called SC (small colony) and LC (large colony) strains of Mycoplasma mycoides subsp. mycoides are said to be indistinguishable by the in vitro serological tests of generally used in mycoplasmology. In mice the immunity given by a single dose of killed LC-strain vaccine against challenge with SC strains is - unlike that given by SC-strain vaccine - only partial. When multiple doses of killed or living vaccines were given, the majority of 13 LC strains still failed to immunize completely against a SC strain. This suggests that, although some protective antigens are shared between both types of strain, at least one of importance is present in the SC strains but absent from the majority of LC strains. The difference between the protective-antigen content of SC and most LC strains is thus qualitative, and not merely quantitative.