Molecular characterization of clustered variants of genes encoding major surface antigens of human Pneumocystis carinii.

A 13-kb genomic fragment from human Pneumocystis carinii was cloned as repetitive DNA. The fragment contains a cluster of three related genes, each 3 kb in size, and the 5' end of a fourth gene. The predicted polypeptide of the first gene in the cluster comprises 1,030 amino acid residues with a total molecular mass of 116 kDa. The gene's predicted amino acid sequence bears 32% identity to predicted sequences of recently described gene fragments of ferret P. carinii, which encode an immunodominant surface glycoprotein (gpA) (P. J. Haidaris, T. W. Wright, F. Gigliotti, and C. G. Haidaris, J. Infect. Dis. 166:1113-1123, 1992), and 36% identity to the predicted sequence of a rat P. carinii major surface glycoprotein gene (msg) (J. A. Kovacs, F. Powell, J. C. Edman, B. Lundgren, A. Martinez, B. Drew, and C. W. Angus, J. Biol. Chem. 268:6034-6040). DNA hybridization showed that sequences related to the cloned msg genes reside on at least 12 chromosomes of human P. carinii at various degrees of multiplicity and/or homology. Affinity-purified antibodies with specificity to a fusion protein made from the human P. carinii msgI gene recognized two bands on a Western immunoblot containing total human P. carinii protein; they also recognized fusion proteins derived from the other two genes of the cluster. Monoclonal antibodies with reactivity to Msg of human P. carinii recognized fusion proteins produced from two msg genes. Fusion proteins were also recognized by sera from healthy humans and from patients. The msg genes are candidates for the development of immunotherapy and subunit vaccines for the treatment and prevention of P. carinii pneumonia.