Serotype 2-specific antigens from ruminant strains of Chlamydia pecorum detected by monoclonal antibodies.

A panel of 25 monoclonal antibodies (MAbs) selected from seven different cellular fusions was used to study the antigenic relationships among a group of 18 ruminant serotype 2 strains of Chlamydia pecorum by indirect microimmunofluorescence test. The antigenic relationships between the strains of C. psittaci serotype 1 and strains of serotype 2 C. pecorum were also studied, as well as the C. pecorum strains and an avian and a feline strain of C. psittaci. Only the genus-specific MAb, used as a positive control, reacted with all the tested strains. Six MAbs reacted with all the C. pecorum serotype 2 strains, but only one of them recognized an 80 kDa protein in Western blot. With these 18 serotype 2 strains, 16 different patterns were established, underlying the high heterogeneity of this group. Only the three caprine strains exhibited the same profile. None of the MAbs reacted with the serotype I strains, or the feline isolate of C. psittaci, but two of them recognized the avian strain. We discuss the possibility that the serotype 2-specific antigens represent C. pecorum species-specific antigens that could be used for diagnosis.