Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UMLS:C0348321 (Haemophilus)
 15,372 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The complement system consists of both plasma and membrane proteins. The former influence the inflammatory response, immune modulation, and host defense. The latter are complement receptors, which mediate the cellular effects of complement activation, and regulatory proteins, which protect host cells from complement-mediated injury. Complement activation occurs via either the classical or the alternative pathway, which converge at the level of C3 and share a sequence of terminal components. Four aspects of the complement cascade are critical to its function and regulation: (i) activation of the classical pathway, (ii) activation of the alternative pathway, (iii) C3 convertase formation and C3 deposition, and (iv) membrane attack complex assembly and insertion. In general, mechanisms evolved by pathogenic microbes to resist the effects of complement are targeted to these four steps. Because individual complement proteins subserve unique functional activities and are activated in a sequential manner, complement deficiency states are associated with predictable defects in complement-dependent functions. These deficiency states can be grouped by which of the above four mechanisms they disrupt. They are distinguished by unique epidemiologic, clinical, and microbiologic features and are most prevalent in patients with certain rheumatologic and infectious diseases. Ethnic background and the incidence of infection are important cofactors determining this prevalence. Although complement undoubtedly plays a role in host defense against many microbial pathogens, it appears most important in protection against encapsulated bacteria, especially Neisseria meningitidis but also Streptococcus pneumoniae, Haemophilus influenzae, and, to a lesser extent, Neisseria gonorrhoeae. The availability of effective polysaccharide vaccines and antibiotics provides an immunologic and chemotherapeutic rationale for preventing and treating infection in patients with these deficiencies.
 ...
PMID:Infectious diseases associated with complement deficiencies. 188 47

The requirement for an intact thiolester bond in C3 for assembly of the membrane attack complex and bactericidal activity was demonstrated in a system permitting only alternative pathway activation. Serum depleted of C3 and C4 by treatment with potassium bromide was reconstituted with forms of C3 with an intact (native C3) or disrupted (NH3.C3) thiolester bond, and bactericidal activity against Haemophilus influenzae b was determined. For strain 885 in high-antibody-containing serum, reconstitution with native C3 was associated with marked bactericidal activity (log10 kill in 60 min 1.01 +/- 0.08) compared with reconstitution with NH3.C3 (log10 kill -0.04 +/- 0.19, p less than 0.001). Similar results were obtained with other strains of H. influenzae b. In serum lacking type-specific antibody no alternative pathway-mediated bactericidal activity was detected against any of the strains examined, even when native C3 was added to KBr serum. These experiments indicate how the biochemical structure of C3 directs its functions; only forms of C3 with an intact thiolester bond, which can covalently bind to bacterial surfaces, can serve as the C5 convertase and generate bacterial activity. In addition these experiments demonstrate an absolute antibody dependence for alternative pathway-mediated bactericidal activity against H. influenzae.
 ...
PMID:Serum bactericidal activity against Haemophilus influenzae. 326 3

A common feature of many different organisms causing bacteremia is the ability to avoid the bactericidal effects of normal human serum. In Haemophilus influenzae encapsulated strains are particularly serum resistant; however, we found that a nonencapsulated strain (R2866) isolated from the blood of an immunocompetent child with meningitis who had been successfully immunized with H. influenzae type b conjugate vaccine was serum resistant. Since serum resistance usually involves circumventing the action of the complement system, we defined the deposition of various complement components on the surfaces of this H. influenzae strain (R2866), a nonencapsulated avirulent laboratory strain (Rd), and a virulent type b encapsulated strain (Eagan). Membrane attack complex (MAC) accumulation correlated with the loss of bacterial viability; correspondingly, the rates of MAC deposition on the serum-sensitive strain Rd and the serum-resistant strains differed. Analysis of cell-associated immunoglobulin G (IgG), C1q, C3b, and C5b indicated that serum-resistant H. influenzae prevents MAC accumulation by delaying the synthesis of C3b through the classical pathway. Among the initiators of the classical pathway, IgG deposition contributes most of the C3 convertase activity necessary to start the cascade ending with MAC deposition. Despite similar IgG binding, strain R2866 delays C3 convertase activity compared to strain Rd. We conclude that strain R2866 can persist in the bloodstream, in part by inhibiting or delaying C3 deposition on the cell surface, escaping complement mediated killing.
 ...
PMID:Serum resistance in an invasive, nontypeable Haemophilus influenzae strain. 1115 57