Filamentous Hemagglutinin of Bordetella bronchiseptica Is Required for Efficient Establishment of Tracheal Colonization

Adherence to ciliated respiratory epithelial cells is considered a critical early step in Bordetella pathogenesis. For Bordetella pertussis, the etiologic agent of whooping cough, several factors have been shown to mediate adherence to cells and cell lines in vitro. These putative adhesins include filamentous hemagglutinin (FHA), fimbriae, pertactin, and pertussis toxin. Determining the precise roles of each of these factors in vivo, however, has been difficult, due in part to the lack of natural-host animal models for use with B. pertussis. Using the closely related species Bordetella bronchiseptica, and by constructing both deletion mutation and ectopic expression mutants, we have shown that FHA is both necessary and sufficient for mediating adherence to a rat lung epithelial (L2) cell line. Using a rat model of respiratory infection, we have shown that FHA is absolutely required, but not sufficient, for tracheal colonization in healthy, unanesthetized animals. FHA was not required for initial tracheal colonization in anesthetized animals, however, suggesting that its role in establishment may be dedicated to overcoming the clearance action of the mucociliary escalator.     

Maximum thigh circumference as an indicator of birth weight

This study had the objective of estimating the strength of association between birth weight and maximum thigh circumference (MTC), sole length, and mid arm circumference (MAC), and on the basis of positive correlation, to identify the ideal anthropometric measurement that can give a reasonable estimate of the birth weight, especially where weight measurement facilities are nonexistent. A random sample of 75 singleton normal neonates was studied who had normal birth in the maternity hospital of the S.K. Institute of Medical Sciences, Srinagar, Kashmir, India, in the first half of 1990. The anthropometric measurements recorded within 24 hours of birth were birth weight, MTC, MAC, and sole length using the left arm and foot. The mean +or- SEM values derived were 3.20 +or- 0.05 kg for weight, 14.68 +or- 0.14 cm for MTC, 7.71 +or- 0.05 cm for sole length, and 9.55 +or- 0.09 cm for MAC. The correlation coefficients of weight were +0.50 for MTC, +0.16 for sole length, and +0.21 for MAC. Only MTC showed a correlation coefficient value of high significance (p .001). MTC was significantly interrelated and interdependent on birth weight inasmuch as MTC can safely be used as an indicator of birth weight in all situations. On the basis of this observation, a regression equation was developed exhibiting the form: Y = (1.48) x +9.4944, where Y represented the MTC. The corresponding values of MTC for birth weight of 2.5 kg and 2.0 kg obtained were 13.644 cm and 12.904 cm, respectively. The lower values constitute the dividing line for low birth weight babies by Indian standards. The comparable values reported by Sharma (1989) were 14.5 cm and 13.5 cm, respectively, presumably due to higher altitude in Kashmir associated with low birth weight. A graphic representation indicating the critical zone was developed for ready reference of paramedical staff in rural areas where weighing facilities for the newborns are not available. MTC, sole length, and MAC are all positively correlated with birth weight.     

Role of Bordetella bronchiseptica fimbriae in tracheal colonization and development of a humoral immune response

Fimbriae are filamentous, cell surface structures which have been proposed to mediate attachment of Bordetella species to respiratory epithelium. Bordetella bronchiseptica has four known fimbrial genes: fim2, fim3, fimX, and fimA. While these genes are unlinked on the chromosome, their protein products are assembled and secreted by a single apparatus encoded by the fimBCD locus. The fimBCD locus is embedded within the fha operon, whose genes encode another putative adhesin, filamentous hemagglutinin (FHA). We have constructed a Fim(-) B. bronchiseptica strain, RB63, by introducing an in-frame deletion extending from fimB through fimD. Western blot analysis showed that RB63 is unable to synthesize fimbriae but is unaffected for FHA expression. Using this mutant, we assessed the role of fimbriae in pathogenesis in vitro and in vivo in natural animal hosts. Although RB63 was not significantly defective in its ability to adhere to various tissue culture cell lines, including human laryngeal HEp-2 cells, it was considerably altered in its ability to cause respiratory tract infections in rats. The number of DeltafimBCD bacteria recovered from the rat trachea at 10 days postinoculation was significantly decreased compared to that of wild-type B. bronchiseptica and was below the limit of detection at 30 and 60 days postinoculation. The number of bacteria recovered from the nasal cavity and larynx was not significantly different between RB63 and the wild-type strain at any time point. The ability of fimbriae to mediate initial attachment to tracheal tissue was tested in an intratracheal inoculation assay. Significantly fewer RB63 than wild-type bacteria were recovered from the tracheas at 24 h after intratracheal inoculation. These results demonstrate that fimbriae are involved in enhancing the ability of B. bronchiseptica to establish tracheal colonization and are essential for persistent colonization at this site. Interestingly, anti-Bordetella serum immunoglobulin M (IgM) levels were significantly lower in animals infected with RB63 than in animals infected with wild-type B. bronchiseptica at 10 days postinoculation. Even at 30 days postinoculation, RB63-infected animals had lower serum anti-Bordetella antibody titers in general. This disparity in antibody profiles suggests that fimbriae are also important for the induction of a humoral immune response.     

CD4+ and CD8+ cytotoxic T lymphocytes may induce mesenchymal cell apoptosis in IgG4-related disease

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