Antigenic similarity between Hammondia hammondi and Toxoplasma gondii tachyzoites

Hammondia hammondi is an obligate heteroxenous intestinal coccidian of cats, sharing many characteristics with Toxoplasma gondii. The tachyzoite stage antigens of T. gondii and H. hammondi were studied by immunofluorescence assays (IFA) and western blotting (WB) techniques to demonstrate antigenic similarities. Five monoclonal antibodies (MAbs), anti-T. gondii antigens, P22, P23, P30, P35, and P43, and mice polyclonal anti-H. hammondi serum were investigated. Antigens of H. hammondi were recognized by anti-P30 MAb both in IFA and in WB and by anti-P22 and anti-P35 MAbs only in IFA. Polyclonal anti-H. hammondi serum revealed many common antigens between the 2 parasites (30, 32, 35, 66, and 90 kDa). The differences of host parasite relationship between these 2 coccidians lead us to suggest that many of these antigens with similar molecular weights are not the same, but homologous, molecules or that they are not the only factors involved in these differences.