Different allotypes of C3 degrade at different rates

Major histocompatibility complex class III (C2, C4, factor B) and C3 gene variants in patients with pulmonary tuberculosis

The complement system is an integral part of the host immune system and plays an immunoregulatory role at the interface of innate and acquired immune responses. Limited data are available on the influence of variations in complement genes in infectious diseases such as pulmonary tuberculosis (PTB). The aim of this study was to investigate the role of genetic variations in complement system components C2, C4, BF, and C3 in PTB (n = 125) compared with healthy controls (n = 125) in the Indian population. The study showed, for the first time, an increased occurrence of null alleles at the C4A, i.e., C4AQ0; an increased frequency of BF*FA and C3*F in patients with PTB compared with healthy individuals, and contributed a risk with odds ratios of 18.16 (95% confidence interval [CI] = 3.0-108.6, p = 0.0004), 2.9 (95% CI = 1.9-4.37, p(c) = 3.15E-06), and 2.26 (95% CI = 1.5-3.3, p(c) = 6.7E-05), respectively. A combinatorial analysis of complement gene variants as risk determinants and their phenotypic effects in various populations may provide unique insights into the genetic basis of susceptibility to PTB.

Critical review of acylation-stimulating protein physiology in humans and rodents

In the last few years, there has been increasing interest in the physiological role of acylation-stimulating protein (ASP). Recent studies in rats and mice, in particular in C3 (-/-) mice that are ASP deficient, have advanced our understanding of the role of ASP. Of note, the background strain of the mice influences the phenotype of delayed postprandial triglyceride clearance in ASP-deficient mice. Administration of ASP in all types of lean and obese mice studied to date, however, enhances postprandial triglyceride clearance. On the other hand, regardless of the background strain, ASP-deficient mice demonstrate reduced body weight, reduced leptin and reduced adipose tissue mass, suggesting that ASP deficiency results in protection against development of obesity. In humans, a number of studies have examined the relationship between ASP, obesity, diabetes and dyslipidemia as well as the influence of diet, exercise and pharmacological therapy. While many of these studies have small subject numbers, interesting observations may help us to better understand the parameters that may influence ASP production and ASP action. The aim of the present review is to provide a comprehensive overview of the recent literature on ASP, with particular emphasis on those studies carried out in rodents and humans.

Studies on the structure of complement C3 and the stability of C3 derived phagocytic ligands C3b/iC3b in SJL/J and BALB/c mice

Female SJL/J mice are more susceptible to development of experimental autoimmune myositis than most other mouse strains. Since complement has been implicated in the pathogenesis of inflammatory muscle disease in humans, quantitative and qualitative studies of complement C3 were undertaken in SJL/J and BALB/c mice to determine whether complement may influence disease susceptibility in SJL/J mice. In accordance with previous studies, mature male and female BALB/c mice were shown to have similar serum C3 concentrations. However, differences were found between mature male and female SJL/J mice. Male SJL/J mice have significantly higher serum C3 concentrations than SJL/J females and both sexes of BALB/c mice suggesting that serum C3 concentration may be variably influenced by sex in some mouse strains. Qualitatively, SJL/J mice were shown to have a different allotypic form of C3 (C3F) compared to the common electrophoretically slow form (C3S) found in BALB/c mice and most other mouse strains. Furthermore, studies on the decay rate of C3 revealed that C3b/iC3b fragments are converted to C3c/d at a faster rate in sera from female SJL/J mice compared to female BALB/c mice. Because removal and solubility of immune complexes is influenced by complement C3, it is possible that the more rapid decay of the phagocytic ligands C3b/iC3b may account for the increased susceptibility to development of autoimmune disease in female SJL/J mice.

The complement system in human reproduction

Regulation of the complement system in reproduction is unique inasmuch as reproductive tissues represent the only condition where allogeneic interactions occur naturally. Both allogeneic extraembryonic membranes and semen that contact and interact with maternal cells and tissues must avert complement-mediated damage to ensure reproductive success. Several regulators of complement activation exist. Membrane cofactor protein (MCP) and decay accelerating factor (DAF) inactivate C3 and C5 convertases on cell surfaces. In addition, CD59 inhibits the membrane attack complex (MAC) of the complement cascade. Strong expression of these membrane glycoproteins by trophoblast and amniotic epithelium has been observed. MCP, DAF, and CD59 likely safeguard extraembryonic tissues from complement damage originating from maternal and fetal blood or amniotic fluid. Different reproductive tract fluids vary in complement levels. With the exception of ovarian follicular fluid, these levels are generally much less than those in blood. Endometrial and cervical content of C3 appear to be regulated by hormones. These observations suggest that the effects of complement activation may vary in reproductive tissues. MCP is absent from the surfaces of oocytes. Sperm express MCP and DAF in discrete areas that would not be associated with the known complement-regulatory functions of these proteins. Seminal plasma contains MCP and the MAC inhibitor SP-40,40 but not DAF.SP-40,40 may exemplify how complement-regulatory proteins perform alternative functions as it interacts with molecules other than complement components. We have reviewed aspects of the complement system that relate to allogeneic interactions in reproduction and that suggest fruitful areas for further research.

Murine candidiasis: sex differences in the severity of tissue lesions are not associated with levels of serum C3 and C5

Mice deficient in the fifth component of complement are known to be extremely susceptible to lethal challenge with Candida albicans. However, male mice, that have significantly higher concentrations of serum C5 than females, were markedly more susceptible to infection. This difference was observed in both susceptible (CBA/H) and resistant (BALB/c) mice. Levels of serum C3 likewise showed no correlation with susceptibility.

Molecular basis of polymorphisms of human complement component C3

C3 exhibits two common allotypic variants that may be separated by gel electrophoresis and are called C3 fast (C3 F) and C3 slow (C3 S). C3 F, the less common variant, occurs at appreciable frequencies only in Caucasoid populations (gene frequency = 0.20). An increased prevalence of the C3 F allele has been reported in patients with partial lipodystrophy, IgA nephropathy, and Indian childhood hepatic cirrhosis. Studies of the genomic organization of the human C3 gene led to the identification of a single change (C to G) between C3 S and C3 F at nucleotide 364 in exon 3. This leads, at the translation level, to the substitution of an arginine residue (positively charged) in C3 S for a glycine residue (neutral) in C3 F. This substitution results in a polymorphic restriction site for the enzyme HhaI. The resulting restriction fragment length polymorphism (RFLP) was investigated using genomic DNA, amplified using the polymerase chain reaction; there was absolute concordance between the genomic polymorphism and the distribution of C3 S and C3 F in 50 normal subjects. The molecular basis of a second structural polymorphism, defined by the monoclonal antibody HAV 4-1, was also characterized. The polymorphic determinant was identified at codon 314 in the exon 9 of the beta chain where a leucine residue (HAV 4-1+) is substituted for a proline residue (HAV 4-1-). Identification of the amino acid sequences of these polymorphic variants will facilitate characterization of possible functional differences between different allotypes of C3. Three RFLPs (BamHI, EcoRI, and SstI) were located to introns in the C3 gene. There was no allelic association between these three RFLPs, or between the RFLPs and the C3 F/S polymorphic site. Genetic equilibration of these polymorphisms has occurred within a gene of 41 kb.

What's new in the role of complement in diseases?

The importance of complement in the potentiation of the immune response is now firmly established. More recently, however, evidence has accumulated which suggests that complement may influence biological events following non-immunologically mediated tissue damage. Several of the many different genetically controlled structural forms of complement components, which are now recognised, have been shown to influence immunoregulation and disease susceptibility. Furthermore, molecular and genetic analyses have revealed that some of the regulatory elements such as S-protein may have multiple biological functions. As a consequence, it is likely that reference to detailed functional and molecular properties of various complement components, with special reference to regulatory elements will provide new insights into mechanisms of pathogenesis of disease.

Complement C3 proteins in psoriasis

A new polymorphism of the complement factor C3 in human plasma was demonstrated by isotachophoresis in agarose gels followed by immunodetection with rabbit anti-human C3c and C3d immunoglobulins. Four bands were detected in the immunoprint of freshly drawn EDTA-plasma, which were C3s1, C3s2, C3f1 and C3f2. At least four additional C3 components in Mg2+ -zymosan activated plasma were present, which were C3b1 to C3b4. The different forms of C3 in frozen and thawed heparin-plasma from 20 patients with psoriasis and 20 healthy individuals were studied from the immunoprint. The total content of C3 components was 29% greater in the patients with psoriasis than controls. The major difference was in the C3b components which were increased by 46%. In psoriatic patients, the two slow C3 components C3s1 and C3s2 were increased by 24 and 56% respectively, when compared with controls. The two fast C3 components C3f1 and C3f2 were decreased to 29 and 37%. The results suggest a direct involvement of the complement factor C3 in psoriasis.

Genetic control of C3 production by the S region of the mouse MHC

The present paper reports evidence indicating that the level of the third complement component (C3) is regulated by the S region of the murine H-2 complex. In fact, using congenic strains of mice we demonstrate that mice with the k haplotype at the S region show high C3 levels, whereas mice with the d haplotype at the S region show low C3 levels.

Electrophoretic polymorphism and molecular structure of equine C3

Plasma or serum samples from 12 Arabian and 181 standardbred horses have been typed using an immunofixation technique to determine electrophoretic polymorphism of equine third complement component (C3). Six distinctly different electrophoretic patterns of equine C3 have been recognized thus far. SDS PAGE analysis of equine C3/anti C3 complexes revealed that the submolecular structure comprised an alpha chain and beta chain of molecular weights approximately 118,000 and 63,000 daltons respectively. The molecular weights of the alpha and beta chains were similar in all electrophoretic variants tested. Family data derived from 73 mares, 21 stallions and 99 offspring suggested that the six electrophoretic phenotypes were inherited by means of three codominant alleles named C3-1, C3-2 and C3-3 at a single autosomal locus.