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PubMedDate not supplied

The properdin system: composition and function.

This article summarized the physicohemical data on the factors which compose the properdin system in guinea pig and man. The following other topics are discussed: (1) Activation of the properdin system; (2) Formation of the initiating and amplification C3 convertases; (3) Formation of the C5 convertase, and (4) Regulatory control mechanisms of the properdin system.

Animals↗
PubMed1992

Role of fibrinogen in complement inhibition by streptococcal M protein.

M protein, the major virulence factor of group A streptococci, has antiopsonic activity in that it inhibits activation of the alternative complement pathway on the streptococcal surface. Two properties of M protein have been claimed to account for the inhibitory activity, namely, (i) its binding affinity for complement factor H, which is an inhibitor of alternative pathway activation, and (ii) its high binding affinity for fibrinogen. We have recently shown that fibrinogen, like M protein, inhibits alternative pathway activation by possessing binding affinity for factor H. Here we report that fibrinogen effectively competes with factor H for binding to M protein but retains its own binding affinity for factor H. The presence of fibrinogen did not significantly affect alternative pathway inhibition on the streptococcal surface.

Antigens, Bacterial↗
PubMed1977

Human lymphocyte complement receptors. Quantitative requirements for C3 of normal and chronic lymphocyte leukemia lymphocytes.

Erythrocytes coated with varying amounts of human complement were used to detect lymphocytes with complement receptors from normal subjects and patients with chronic lymphocytic leukemia. The relationship between the percentage of lymphocytes rosetting and the quantity of C3 present on complement-coated erythrocytes were studied. Small quantities of C3 (less than 5 fg/erythrocyte) caused maximal rosetting of normal lymphocytes. Maximal rosetting with chronic lymphocytic leukemia lymphocytes was not reached until much greater amounts of C3 were used to coat the erythrocytes. This difference in sensitivity to erythrocyte-bound complement was not due to an increased fraction of complement receptor-bearing cells in the leukemic patients. This loss of sensitivity of the chronic lymphocytic leukemia lymphocyte for complement may play a role in the immune deficiency present in this disease.

Cell Membrane↗
PubMed1992

Pleural SC5b-9 in differential diagnosis of tuberculous, malignant, and other effusions.

A monoclonal antibody against soluble phase-terminal complement complex (SC5b-9) was used to try to differentiate pleural effusions of tuberculous vs malignant and other origin. Effusions of tuberculous origin showed a significantly higher SC5b-9 level than did plasma, suggesting activation of complement in the pleural space. All 26 patients with tuberculous effusions showed SC5b-9 levels in pleural fluid exceeding 2.0 mg/L, while 20 with malignant effusions had levels less than 2.0 mg/L. However, rheumatoid, some parapneumonic, and treated malignant effusions showed SC5b-9 levels above 2.0 mg/L. Considering a value exceeding 2.0 mg/L, the specificity and sensitivity of the SC5b-9 estimation in tuberculosis were 0.74 and 1.0, respectively. The mean values for C4d and Bb fragments of complement were significantly (p < 0.05) higher in the tuberculous than in the malignant effusions. However, the values for Bb in 16 (62 percent) of the 26 patients with tuberculous or malignant effusions were in the same range. The activity of adenosine deaminase (ADA) was higher in the tuberculous than in the malignant effusions. While 18 of 26 patients with tuberculous effusions showed an ADA value exceeding 50 mU/ml, the estimated cutoff point (sensitivity = 0.69), 35 of the 36 nontuberculous effusions showed a true negative value (specificity = 0.97). A correlation between ADA and SC5b-9 values was observed in pleural effusions. These observations suggest that the estimation of SC5b-9 in pleural fluid presents a new approach to differentiating tuberculous vs malignant effusions.

Adenosine Deaminase↗
PubMed1979

Activation of the alternative complement pathway by Torulopsis glabrata.

Torulopsis glabrata is a yeast-like fungus with increasing importance as an opportunistic human pathogen. The role of serum complement in resistance to this infection was studied by chemotactic and opsonic assays. The results indicate that T. glabrata activates complement via the alternative pathway. This may be an important mechanism in host immunity to this fungus.

Candida↗
PubMed1976

A phagocytosis-enhancing factor in human plasma.

A phagocytosis-enhancing factor (PEF) with the capacity to stimulate the ingestion of sensitized sheep erythrocytes by human polymorphonuclear and mononuclear leucocytes has been isolated from human plasma by chromatography on DEAE-cellulose and filtration on Sephadex G-150 and Sephadex G-100. PEF is a protein of approximately 70,000 molecular weight which is susceptible to inactivation by heating at 60 degrees or by tryptic digestion. PEF promotes phagocytosis of erythrocytes sensitized with intact 7S antibody or bearing the C3b complement fragment, but not of unsensitized erythrocytes or erythrocytes sensitized with 19S antibody. The specificity of PEF interaction with target erythrocytes and the persistence of its stimulatory effect after the target cells are washed suggest that it promotes phagocytosis by an action on the erythrocytes.

Antibodies↗
PubMed1992

[Recent advances in xenotransplantation].

Interest in xenotransplantation has dramatically increased in the past 4 years, focusing on the potential use as donors of distantly related animals such as pigs (discordant xenografts). The major barrier is hyperacute rejection. The mechanisms responsible for this rejection include: specific reaction of the recipient's natural antibodies with antigens in the donor's organ, direct activation of the recipient's complement system by endothelial cells in the donor's organ, and/or relative failure of complement inhibitory proteins in the donor's organ to impede activation of the recipient's complement system. In case of vascularized xenograft, the temporary depletion of anti-donor antibodies (anti-ABH or anti-HLA class I) from a graft recipient may allow the long term survival of the graft despite a possible return of the antibodies to the circulation. This phenomenon is called accommodation. The mechanisms involved could be: the endothelial cells in a graft develop a resistance to complement mediated injury; the antigens expressed on the blood vessels become modulated or changed; the natural antibody repertoire changes in such a way that there are fewer anti-donor antibodies. The accommodation phenomenon encourages the view that the barrier to xenotransplantation is not immutable.

Complement C3b↗
PubMed1979

A comparison of immunologic profiles and their influence on bacteremia in surgical patients with a high risk of infection.

Prospective sequential studies of the antibacterial function of neutrophils, lymphocyte responsiveness, opsonic capacity of serum and serum levels of C3(B), properdin, factor B, IgG, and albumin were made in 32 patients with severe burn injury (greater than or equal to 45%), 21 patients with severe multisystem traumatic injury, 20 high-risk, infected patients, and 22 renal transplant patients. Fifty-five episodes of bacteremia occurred in 37 of the 95 patients. Abnormal neutrophil function was clearly associated as a predisposing factor to these episodes, whereas there was no association between bacteremia and low serum levels of C3, IgG, factor B, or properdin. C3, factor B, and IgG usually rose following bacteremia as acute phase proteins, but there was evidence of a consumptive opsoninopathy in 11% of episodes. Defective opsonization was associated with a high risk of bacteremia only when there was a coexisting abnormality of neutrophil function (88% of such patients became bacteremic). None of 27 nonburned patients tested with delayed hypersensitivity antigens responded normally, and there was regularly depression of lymphocyte responsiveness to phytohemagglutinin-A and concanavalin-A in a whole blood assay related to serum immunosuppressive factors, but poor responsiveness was not associated with bacteremia.

Adolescent↗
PubMedDate not supplied

The biological role of the complement system and the clinical importance of complement measurements.

Properties of serum proteins belonging to the complement system, two pathways of the complement activation (classical and alternative pathway) as well as the physiological role of the complement system are discussed. Complement has essential importance in some physiological processes: In the induction of the humoral immune response, in the elimination of immune complexes and in the protection against bacterial and viral infections. After a short discussion of the genetics of the complement system, the principle and possibilities of clinical applications of the complement measurements are described. Finally, different approaches to the therapeutic manipulation of the complement system are discussed.

Angioedema↗