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PubMed1987

Macrophage C1q: characterization of a membrane form of C1q and of multimers of C1q subunits.

It has been shown recently that C1q, a subcomponent of the first component of the classical complement pathway, is synthesized by macrophages and that endogenous C1q is detectable on the macrophage membrane. In this report, we demonstrate that membrane-associated C1q, which contains the A, B, and C chains of C1q, is structurally distinct from fluid-phase C1q in that the B chain of the membrane species is approximately 1000 m.w. less than its fluid-phase counterpart. By using biosynthetically ([3H]proline) labeled C1q from guinea pig peritoneal macrophages, we found that the membrane form of C1q is derived from already secreted C1q. The demonstration of a distinct membrane form of C1q supports earlier functional studies which implicated C1q as a membrane-associated molecule with receptor functions for those molecules which also interact with fluid-phase C1q, such as polyanions, immune complexes, and bacteria. Furthermore, we show that, in the vicinity of macrophages, C1q is very susceptible to oxidation manifested by the formation of disulfide bonds. By SDS-PAGE (nonreduced and reduced), we demonstrate the existence of disulfide-linked multimers (180,000 m.w., 360,000 m.w.) which are composed of the A, B, and C chains of C1q.

Animals↗
PubMed1987

Quantification of the complement receptor function on polymorphonuclear leukocytes: its significance in patients with systemic lupus erythematosus.

The function of complement receptors (CR1) on polymorphonuclear leukocytes (PMN) was assessed by C3b mediated binding of immune complexes (IC) to PMN. The binding of IC to CR1 on PMN depends on the activation of the classical complement pathway and was inhibited by the antibody to CR1 or C3b. CR1 function of PMN from patients with systemic lupus erythematosus was reduced compared with those from normal controls or patients with rheumatoid arthritis.

Antibodies, Monoclonal↗
PubMed1986

[Studies on the interaction between cells infected with measles virus and anti-measles antibody. I. Cytotoxic antibody activity of sera obtained from patients with natural measles and subacute sclerosing panencephalitis by use of chronically infected cell lines].

Sera obtained from patients with natural measles and subacute sclerosing panencephalitis (SSPE) showed cytotoxic activity in the presence of complement on cells persistently infected with either measles virus (Schwarz and TYCSA strains) or SSPE virus (Halle and Mantooth strains). The cytotoxic activity was demonstrated in both IgG and IgM fractions of measles convalescent sera, but only in IgG fraction of SSPE sera. Measles convalescent sera completely lost the cytotoxic activity to all carrier cell lines, when absorbed with any one of the cell lines, indicating that the viral surface antigens of these cell lines infected with measles or SSPE virus were identical. On the other hand, the cytotoxic activity of SSPE sera could not be readily absorbed with these cells. Thus, the affinity of SSPE sera for the viral surface antigens might be lower than that of measles convalescent sera.

Adult↗
PubMed1986

[Pruritus and tardive cutaneous porphyria].

Pruritus was present in one half of our cases and ran parallel to the disease, thereby suggesting a causal relationship between it and PCT. Moreover, no correlations could be established between pruritus and the patients' sex, associated treatments (oestrogens, etc.) or underlying disease (liver damage, diabetes mellitus, cancer, hypersideraemia), nor between pruritus and the form of PCT (sporadic or familial) and the levels of urinary porphyrins. Pruritus localized to sun-exposed skin areas belongs to the category of phototoxic symptoms, although a burning sensation is more often observed in such cases, but this cannot explain the generalized pruritus. Immunoglobulin and complement deposits in the vessel walls have been demonstrated in PCT. In addition, the serum of PCT patients may, when irradiated, activate the classical complement pathway, thus promoting the release of mediators. Pro-inflammatory enzymes probably play a secondary role.

Aged↗
PubMed1986

Activator-bound C1 is less susceptible to inactivation by C1 inhibition than is fluid-phase C1.

Parameters that influence the effective interaction of C1 with the serum regulatory glycoprotein C1 Inhibitor were investigated. C1 that bound to activator particles EAC4 or EA was strikingly less susceptible to inactivation by C1 Inhibitor than was fluid-phase C1. By using the conventional hemolytic assay, the concentrations of C1 Inhibitor required for inhibition of C1 bound to EAC4 were 1000-fold higher than those required for fluid-phase C1. With EA as the activator (and indicator) particle, 17- to 75-fold higher concentrations of C1 Inhibitor were required to inhibit bound vs free C1. These findings suggest that, on binding to these particulate immune complexes, the domain of the C1 molecule capable of interacting with C1 Inhibitor is less available for binding than when C1 is in fluid phase. Alternatively, the conformation of C1 may be altered when bound to EA or EAC4, resulting in a lower association constant of C1 Inhibitor for C1. As assessed by inhibition of classical complement pathway hemolysis, the inhibition of the enzymatic activity of C1 by C1 Inhibitor (both in the fluid phase and particle-bound) was markedly dependent on the concentration of the reactants. Incubation of C1 and C1 Inhibitor at serum concentrations resulted in the inhibition of more than 10 times the amount of C1 hemolytic activity than that which occurred when the same ratio of components was incubated at the more dilute concentrations used in the conventional hemolytic assays. These findings have allowed for the development of a more sensitive and rapid assay for C1 Inhibitor function.

Complement Activating Enzymes↗
PubMed1985

Reduced complement-mediated immune complex solubilization in leprosy patients.

The ability of sera from leprosy patients to solubilize immune precipitates in vitro through the complement system was studied. The solubilizing capacity of sera from patients who did not have any reactions during 2 years or more after starting chemotherapy was comparable with that of normal laboratory volunteers. On the other hand, sera from borderline tuberculoid and lepromatous leprosy patients in reaction had markedly decreased levels of solubilization. Their total and the alternative pathway haemolytic levels did not show a corresponding decrease. Although the circulating immune complexes and serum C3d of these patients came down after the subsidence of reaction, their solubilization remained consistently low during a 3 month follow-up period.

Antigen-Antibody Complex↗
PubMed1985

Paroxysmal nocturnal haemoglobinuria.

The analysis of the abnormality of the membrane in paroxysmal nocturnal haemoglobinuria is an exercise in complexity complexified--of Ossa atop Pelion. To understand it, we will need to understand fully the complexities of the complement system and the complexities of the structure of the membrane and the complexity of their concert interaction. Added to this are the complexities of growth and development of the haematopoietic cells--a problem we have not discussed at all despite its importance in the pathophysiology of PNH. It is little wonder that a disease which is uncommon but not rare continues to fascinate investigators from a wide variety of disciplines. If, as has been (falsely) said, more people studied the disease than had it, it would be because it presents questions of such fundamental interest. In unravelling its mysteries, many problems related to the normal functioning of cells, complement and a haematopoiesis have been and will continue to be solved.

Acetylcholinesterase↗