Abstract
Intravenous injections of Mycoplasma pneumoniae, as well as of Listeria monocytogenes and Streptococcus MG, stimulated the production of CA in rabbits. Absorption experiments indicated that these microorganisms possess antigens related to the red cell I antigen, most strongly represented in M. pneumoniae. It is suggested that the CA production during primary atypical pneuomonia caused by M. pneumoniae may be triggered off by an I‐like antigen present in this microorganism.