Immunodominant domains present on the Bordetella pertussis vaccine component filamentous hemagglutinin.

To identify immunologically important domains on filamentous hemagglutinin (FHA), a Bordetella pertussis protein included in new acellular pertussis vaccines (ACPVs), a series of monoclonal antibodies, sera from infants vaccinated with ACPVs or whole cell pertussis vaccine (WCPV), and sera from patients with pertussis were analyzed by immunoblots containing FHA fragments and recombinant FHA proteins. Immunodominant domains located at the COOH-terminus of FHA (type I domain) and near the NH2-terminus (type II domain) were defined by the reactivity with monoclonal antibodies. The sera from patients with pertussis and sera from infants vaccinated with WCPV or with 6 different investigational ACPVs specifically recognized well-defined regions within the type I and type II domains. Identification of these prominent immunologic epitopes on FHA should be useful for the construction of more well-defined pertussis vaccines and for the interpretation of human serologic responses, which may correlate with efficacy of pertussis vaccines.

Identification of a heparin-binding hemagglutinin present in mycobacteria.

Adherence to mammalian host tissues is an important virulence trait in microbial pathogenesis, yet little is known about the adherence mechanisms of mycobacteria. Here, we show that binding of mycobacteria to epithelial cells but not to macrophages can be specifically inhibited by sulfated carbohydrates. Using heparin-Sepharose chromatography, a 28-kD heparin-binding protein was purified from culture supernatants and cell extracts of Mycobacterium bovis and Mycobacterium tuberculosis. This protein, designated heparin-binding hemagglutinin (HBHA), promotes the agglutination of rabbit erythrocytes, which is specifically inhibited by sulfated carbohydrates. HBHA also induce mycobacterial aggregation, suggesting that it can mediate bacteria-bacteria interactions as well. Hemagglutination, mycobacterial aggregation, as well as attachment to epithelial cells are specifically inhibited in the presence of anti-HBHA antibodies. Immunoelectron microscopy using anti-HBHA monoclonal antibodies revealed that the protein is surface exposed, consistent with a role in adherence. Immunoblot analyses using antigen-specific antibodies indicated that HBHA is different from the fibronectin-binding proteins of the antigen 85 complex and p55, and comparison of the NH2-terminal amino acid sequence of purified HBHA with the protein sequence data bases did not reveal any significant similarity with other known proteins. Sera from tuberculosis patients but not from healthy individuals were found to recognize HBHA, indicating its immunogenicity in humans during mycobacterial infections. Identification of putative mycobacterial adhesins, such as the one described in this report, may provide the basis for the development of new therapeutic and prophylactic strategies against mycobacterial diseases.

Age-dependent humoral responses of children to mycobacterial antigens.

In the United States, disseminated infection with environmental mycobacteria, including the Mycobacterium avium complex, is the most common opportunistic bacterial infection seen in AIDS patients. However, the source and relative degree of exposure to environmental mycobacteria during childhood are unknown. To examine the age-related exposure to mycobacteria, we obtained serum samples from 150 children ranging in age from 6 months to 18 years. Each sample was tested against both M. avium (serovar 1) sonic extracts and mycobacterial lipoarabinomannan, using an enzyme-linked immunosorbent assay (ELISA). All serum samples were also subjected to immunoblot analysis with the sonic extract antigen. These studies established that elevated ELISA values (P < 0.0001) and increased immunoblot reactivity (P < 0.0001) against mycobacterial antigens were both associated with increasing age. The seroreactivity differences were most striking when comparing the age groups of children below the age of 6 with the older age groups. Our results suggest that the development of humoral immune responses to mycobacterial antigens in children correlates with increasing age and that there may be an environmental factor predisposing to mycobacterial exposure which is related to advancing age.