C4, one of the early components of the classical complement pathway, is encoded within the class III region of the major histocompatibility complex of man at two highly polymorphic loci, C4A and C4B. Widespread use of C4 typing is, however, hindered by the lack of objective standardized methods.
Objective evaluation of the C4 typing pattern by densitometry was first proposed by Christiansen and coworkers (1983) and Zhang and co-workers (1988). The use of this method in finding homoduplications of the C4 genes was described in a recent abstract (Truedsson et al. 1987). To the best of our knowledge, however, no systematic comparative study of densitometric vs visual evaluation of C4 typing has been performed. In the present work we measured the relative intensities of different C4A and C4B bands by densitometric scanning of pattern of 191 plasma samples.
Ethylenediaminetetraacetate (EDTA) plasma samples were collected from paternity studies and stored at -70 °C until used. C4 phenotyping was carried out by the method of Awdeh and Alper (1980) using carboxypeptidase/B treatment as described by Sire and Cross (1986). Intensity of the Coomassie Brillant Blue R-250 staining of C4 bands in the gel was measured by scanning the gels with a Cello3 densitometer (Shandon, Ltd., Astmoor, United Kingdom). The C4A and C4B regions were evaluated as a whole, and the results were given as the staining intensity of the C4A region in the percentage of staining of the whole gel. Calculations were carried out by an IBM compatible computer (PC-420XT) using STATGRAPHICS program (STSC Inc., Plus+Ware, Braegen Grp. Inc., Toronto, Canada). Means of the groups were compared by the Mann-Whitney-Wilcoxon test. The probability that a value was correctly assigned to a group was calculated by the tail area probability analysis.
Neuraminidase-treated EDTA plasma samples of 94 persons were typed for C4. The patterns were evaluated