The relevance of cyst and trophozoite antigens in the serodiagnosis of Pneumocystis carinii infection
P. carinii cysts and trophozoites from infected rat lungs were separated and used as antigen sources in immunoblotting. Rat hyperimmune antisera against cyst-rich and trophozoite-rich antigens demonstrated strong bands at 50-60 and 104 kDa in cyst and trophozoite antigen. Proteins of 88,81,73,69,63 and 37 kDa were only found in trophozoite-antigen. Proteins of 81 and 63 kDa were only demonstrated by rat anti-trophozoite antisera and appeared to be specifically associated with trophozoites. When sera from immunosuppressed rats with and without PCP were tested, only 2/14 PCP positive rats demonstrated antibodies to 50-60 kDa proteins in cyst-rich antigen. With trophozoite-rich antigen 11/24 with PCP and 1/8 without PCP had antibodies to 50-60 and 104 kDa antigens. Antibodies to 81 and 63 kDa antigens were demonstrated in 15/24 PCP positive rats and none of the PCP negative animals. Demonstration of antibodies to 63 and or 81 kDa trophozoite proteins seemed to be useful markers of current infection in the rat model. With human sera trophozoite antigen was also more reactive than cyst antigen in immunoblotting. Patients with proven, probable and possible P. carinii infection demonstrated IgG antibody to 50-60,61-70,82,95,99,116 kDa proteins. Antibody to the 82 kDa protein was prominent in PCP patients and was demonstrated in 9/18 sera from patients with proven PCP and 6/12 from patients with probable PCP compared to 15/39 from patients with possible P. carinii infection. IgM and IgA antibodies to the same proteins were demonstrated in 2/14 sera from patients with proven and probable P. carinii infection. This thesis demonstrates that PCP patients can make an immunological response to infection and trophozoites, not cysts, provide the most useful source of antigen for serology.