Comparison of hemagglutinating pili of Haemophilus influenzae type b with similar structures of nontypeable H. influenzae

Abstract

Thirty-eight clinical isolates of nontypeable Haemophilus influenzae were tested for the presence of hemagglutinating pili similar to those of H. influenzae type b (Hib) that mediate buccal epithelial cell adherence. Four endogenously hemagglutinating (HA') strains were identified, and eight additional HA' variants were obtained from HAstrains by erythrocyte enrichment. All 12 HA' nontypeable H. influenzae isolates bound antisera directed against denatured pilins of Hib, but none bound antisera against assembled native pili of Hib. In erythrocyteand buccal-cell-binding assays, HA' nontypeable H. influenzae binding was reduced compared with HA' Hib binding and was not significantly different from HAnontypeable H. influenzae binding. Both HAand HA' nontypeable H. influenzae binding was increased over binding of HA-Hib. HA' nontypeable H. influenzae strains agglutinated adult erythrocytes that possess the Anton antigen, which is thought to be the receptor for Hib pili, and did not agglutinate cord or Lu(a-b-) dominant erythrocytes, which lack the Anton antigen. Electron microscopy of HAand HA' variants of three nontypeable H. influenzae strains showed few or no surface appendages on the HA-organisms, but piluslike structures were seen on many organisms from two HA' nontypeable H. influenzae strains and on a few organisms from one strain. Thus, nontypeable H. influenzae appears to possess structures that are immunologically similar to the pilins that make up the hemagglutinating pili of Hib. However, nontypeable H. influenzae appears to also possess mechanisms for erythrocyte and buccal cell adherence that are not directly correlated with the presence of a hemagglutinating pilus. 17).

Molecular determinants of the pathogenesis of disease due to non-typable Haemophilus influenzae

“…in£uenzae pili were initially puri¢ed from type b strain AO2 and were found to be composed of repeating 25-kDa proteins with amino acid sequence similarity to Escherichia coli P pilus, type 1 pilus, and F17 pilus subunits [76]. Surface organelles with similar morphology and adhesive activity have been described in other type b strains and in a minority of non-typable strains [77]. Brinton and coworkers have distinguished at least fourteen serological types of hemagglutinating pili, designated LKP (long, thick, hemagglutination-positive) serotypes [78].…”

“…In contrast, pili from non-typable strains are more diverse [78]. Although the major structural subunits from di¡erent strains show substantial similarity in amino acid sequence, antiserum raised against a particular piliated strain is usually not broadly reactive, indicating that immunodominant epitopes in the mature pilus structure are likely conformational and strain-speci¢c in nature [77,79]. As an example, in the chinchilla model of otitis media, Karasic et al found that immunization with puri¢ed pili protected animals from challenge with the homologous piliated strain, but failed to protect from challenge with a heterologous piliated strain [80].…”

“…On the basis of analysis by Farley et al, the frequency of variation is believed to be roughly 10 3Q to 10 3R per generation in both directions [186]. Although only a subset of non-typable isolates contain the pilus gene cluster, there is evidence for phase variation in these strains as well [77]. Interestingly, nasopharyngeal isolates with the pilus gene cluster often express pili, while matched middle ear isolates typically lack pili [187].…”

Evidence for donor strand complementation in the biogenesis of Haemophilus influenzae haemagglutinating pili

“…Diverse isolates of H. influenzae express a variety of pilus and non‐pilus adhesive factors (Rao et al ., 1999) involved in recognition of specific eukaryotic receptor motifs (Karlsson, 1989; Hultgren et al ., 1996). Perhaps best‐characterized among H. influenzae adhesins are haemagglutinating pili, which are expressed by encapsulated and a subset of non‐encapsulated (non‐typable) strains (Stull et al ., 1984; Gilsdorf et al ., 1992; Krasan et al ., 1999). These structures agglutinate AnWj‐positive erythrocytes and mediate attachment to human oropharyngeal cells and respiratory tissue in organ culture (van Alphen et al ., 1986; Loeb et al ., 1988; Farley et al ., 1990; Read et al ., 1991).…”

Moraxella (Branhamella) catarrhalis Adherence to Human Bronchial and Oropharyngeal Cells: The Role of Adherence in Lower Respiratory Tract Infections

“…The present data also show no difference in binding to upper airway cells between the fimbriated and nonfimbriated strains. This was analogous to nontypable H. influenzae, which had a fimbriae-independent mechanism for binding to respiratory epithelium (4,8).…”