CHARACTERIZATION OF A NOVEL LIPOPROTEIN EXPRESSED BY HAEMOPHILUS-DUCREYI

Pooled sera from patients with chancroid contain antibodies to a Haemo philus dacreyi antigen with an approximate molecular weight of 28,000 (28K). Rabbit polyclonal serum that reacts to a 28K protein can be use d to detect H. ducreyi in clinical samples. A monoclonal antibody, des ignated 5C9, bound to a 28K outer membrane protein and to 35 of 35 H. ducreyi isolates with diverse geographic origins and did not bind to m any species of the families Pasteurellaceae, Neisseriaceae, and Entero bacteriaceae or to Corynebacterium and Candida species strains. A 5C9- reactive phage was recovered from a genomic library and the gene encod ing the 28K protein was localized to a 626-bp open reading frame, desi gnated hlp, for H. ducreyi lipoprotein, Translation of hip predicted a 23K polypeptide that contained a lipoprotein processing site. Escheri chia coli transformed with a plasmid containing hlp expressed a novel, membrane-associated protein that could be labeled with [H-3]palmitic acid. In H. ducreyi, processing of Hlp was inhibited by globomycin. Da tabase searches found no homologies to hip or to the predicted Hip ami no acid sequence. Restriction enzyme analysis indicated that hip was c onserved among H. ducreyi isolates, Serum samples from patients with c hancroid and other genital ulcer diseases and from normal subjects con tained antibodies that bound to purified, recombinant Hip. Although mo noclonal antibody 5C9 recognizes a species-specific epitope of a uniqu e H. ducreyi lipoprotein, the presence of serum antibodies to Hip may not indicate previous infection with H. ducreyi.