Serodiagnostic potential of culture filtrate antigens of Mycobacterium tuberculosis

Our studies of the humoral responses of tuberculosis (TB) patients have def ined the repertoire of culture filtrate antigens of Mycobacterium tuberculo sis that are recognized by antibodies from cavitary and noncavitary TB pati ents and demonstrated that the profile of antigens recognized changes with disease progression (K. Samanich et al., J. Infect. Dis. 178:1534-1538, 199 8). We have identified several antigens with strong serodiagnostic potentia l. In the present study we hare evaluated the reactivity of cohorts of huma n immunodeficiency virus (HIV)-negative, smear-positive; HIV-negative, smea r-negative; and HIV-infected TB patients, with three of the candidate antig ens. an 88-kDa protein, antigen (Ag) 85C, and MPT32, and compared the react ivity of the same patient cohort with the 38-kDa antigen and Ag 85A, We hav e also compared the reactivity of native Ag 85C and MPT32 with their recomb inant counterparts. The evaluation of the reactivity was done by a modified enzyme-linked immunosorbent assay described earlier (S. Laal et al,, Clin, Diag, Lab. Immunol, 4:49-56, 1997, in which all sera are preadsorbed again st Escherichia coli lysates to reduce the levels of cross-reactive antibodi es. Our results demonstrate that (i) antigens identified on the basis of th eir reactivity with TB patients' sera pro,ide high sensitivities for serodi agnosis, (ii) recombinant Ag 85C and MPT32, expressed in E. coli, show redu ced reactivity with human TB sera, and (iii) of the panel of antigens teste d, the 88-kDa protein is the most promising candidate for serodiagnosis of TB in HIV-infected individuals. Moreover, these results reaffirm that both the extent of the disease and the bacterial load may play a role in determi ning the antigen profile recognized by antibodies.