Rickettsia IFA substrate slides are available for all or most of the officially validated species, 16 of which are currently recognized as human pathogens. Due to the Class 3 nature of these organisms, our traditional substrate antigens have been formalin-inactivated prior to slide preparation.These slides contain Vero-76 cells with 30-40 infected cells per field when using a 40X lens.
Our new larger BSL3 facilities are allowing us the opportunity to prepare slides with infected substrate cells grown in situ within the slide wells. This line is being retooled to use acetone-fixation as the inactivation step and will be currently available for a a growing number of species. The effect is subtle, but worth the effort as an IgG screening protocol.
Due to the presence of an immunodominant lipopolysaccharide (LPS) antigen on native spotted fever Rickettsia, the occurrance of false-positives due to this antigen compromises the value of both IFA and MIF protocols for IgM testing. We strongly recommend ELISA protocols using our purified protein (OmpA and OmpB) antigens for IgM testing. The LPS antigen has been removed to provide an assay free of false-positive reactions.