The molecular structure of different polymorphic forms of canine C3 and C4

Serum concentrations of complement C3 and C4 in dogs with idiopathic epilepsy

BACKGROUND

High concentrations of complement factors are presented in serum of animal epilepsy models and human patients with epilepsy.

OBJECTIVES

To determine whether complement dysregulation occurs in dogs with idiopathic epilepsy (IE).

ANIMALS

The study included 49 dogs with IE subgrouped into treatment (n = 19), and nontreatment (n = 30), and 29 healthy dogs.

METHODS

In this case-control study, the serum concentrations of the third (C3) and fourth (C4) components of the complement system were measured using a canine-specific ELISA kit.

RESULTS

Serum C3 and C4 concentrations were significantly higher in dogs with IE (C3, median; 4.901 [IQR; 3.915-6.673] mg/mL, P < .001; C4, 0.327 [0.134-0.557] mg/mL, P = .03) than in healthy control dogs (C3, 3.550 [3.075-4.191] mg/mL; C4, 0.267 [0.131-0.427] mg/mL). No significant differences were observed in serum C3 and C4 concentrations between dogs in the treatment (C3, median; 4.894 [IQR; 4.192-5.715] mg/mL; C4, 0.427 [0.143-0.586] mg/mL) and nontreatment groups (C3, 5.051 [3.702-7.132] mg/mL; C4, 0.258 [0.130-0.489] mg/mL). Dogs with a seizure frequency >3 times/month had significantly higher serum C3 (6.461 [4.695-8.735] mg/mL; P < .01) and C4 (0.451 [0.163-0.675] mg/mL; P = .01) concentrations than those with a seizure frequency ≤3 times/month (C3, 3.859 [3.464-5.142] mg/mL; C4, 0.161 [0.100-0.325] mg/mL).

CONCLUSIONS AND CLINICAL IMPORTANCE

Dysregulation of classical complement pathway was identified in IE dogs. Serum C3 and C4 concentrations could be diagnostic biomarkers for IE in dogs with higher seizure frequency.

The complement component C4 of mammals

Human complement component C4 is coded by tandem genes located in the HLA class III region. The products of the two genes, C4A and C4B, are different in their activity. This difference is due to a degree of 'substrate' specificity in the covalent binding reactions of the two isotypes. Mouse also has a duplicated locus, but only one gene produces active C4, while the other codes for the closely related sex-limited protein (Slp). In order to gain some insight into the evolutionary history of the duplicated C4 locus, we have purified C4 from a number of other mammalian species, and tested their binding specificities. Like man, chimpanzee and rhesus monkey appear to produce two C4 types with reactivities similar to C4A and C4B. Rat, guinea pig, whale, rabbit, dog and pig each expresses C4 with a single binding specificity, which is C4B-like. Sheep and cattle express two C4 types, one C4B-like, the other C4A-like, in their binding properties. These results suggest that more than one locus may be present in these species. If this is so, then the duplication of the C4 locus is either very ancient, having occurred before the divergence of the modern mammals, or there have been three separate duplication events in the lines leading to the primates, rodents and ungulates.

Statement on the nomenclature of dog C4 allotypes

As a collaborative work of three laboratories the polymorphism of the canine fourth complement component (C4) was studied in a total of 131 unrelated dogs from different breeds and mongrels. Using high voltage electrophoresis followed by an immunoblotting technique, we detected eight distinct variants. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) of canine C4 showed an additional heterogeneity of the alpha and gamma chains which resulted in a total of 11 variants in the population studied. So that more precise information concerning the respective C4 allotypes will be available, a nomenclature is proposed designating not only the migration pattern of the C4 variants in agarose gels but also the heterogeneity of the C4 chains observed in SDS-PAGE.

A review of major histocompatibility complex-disease associations in man and dog

The organization and biology of the Major Histocompatibility Complexes (MHC) of man (HLA) and dog (DLA) are reviewed, and a summary is presented of laboratory techniques used to define allotypes. The nomenclature of this field and the mechanisms of disease association with the MHC are discussed. Currently recognized HLA-disease associations are enumerated, with emphasis on the value of the complement C4 marker. DLA-disease association studies into autoimmune disease, allergy and neoplasia are reviewed.

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.