Associations of properdin factor B with melanoma

Ancestry reported by white adults with cutaneous melanoma and control subjects in central Alabama

Background

We sought to evaluate the hypothesis that the high incidence of cutaneous melanoma in white persons in central Alabama is associated with a predominance of Irish and Scots descent.

Methods

Frequencies of country of ancestry reports were tabulated. The reports were also converted to scores that reflect proportional countries of ancestry in individuals. Using the scores, we computed aggregate country of ancestry indices as estimates of group ancestry composition. HLA-DRB1*04 allele frequencies and relationships to countries of ancestry were compared in probands and controls. Results were compared to those of European populations with HLA-DRB1*04 frequencies.

Results

Ninety evaluable adult white cutaneous melanoma probands and 324 adult white controls reported countries of ancestry of their grandparents. The respective frequencies of Ireland, and Scotland and "British Isles" reported countries of ancestry were significantly greater in probands than in controls. The respective frequencies of Wales, France, Italy and Poland were significantly greater in controls. 16.7% of melanoma probands and 23.8% of controls reported "Native American" ancestry; the corresponding "Native American" country of ancestry index was not significantly different in probands and controls. The frequency of HLA-DRB1*04 was significantly greater in probands, but was not significantly associated with individual or aggregate countries of ancestry. The frequency of DRB1*04 observed in Alabama was compared to DRB1*04 frequencies reported from England, Wales, Ireland, Orkney Island, France, Germany, and Australia.

Conclusion

White adults with cutaneous melanoma in central Alabama have a predominance of Irish, Scots, and "British Isles" ancestry and HLA-DRB1*04 that likely contributes to their high incidence of cutaneous melanoma.

DNA polymorphism of the C2 locus

The extent of the C2 locus in the HLA class III region has been determined by Southern blotting techniques and by DNA sequence analysis. The gene is 18 kb in length and therefore provides a marked contrast to the adjacent factor B gene of 6 kb. A novel restriction fragment length polymorphism (RFLP) has been identified using the endonuclease Sst I and a genomic probe derived from the 5' region of the C2 gene. Four variants have been detected in a sample of unrelated individuals with haplotypes carrying the C2C allele. Further analysis using C2 and factor B cDNA probes has determined the relationship between this and the other RFLPs previously identified in this region of the genome. Together, the three polymorphisms identified so far make the subdivision of previously indistinguishable haplotypes possible. They therefore constitute a series of markers which increase the resolution of genetic variation in the C2 locus and they may be important in studies of diseases associated with this region of the major histocompatibility complex.

The structure and genetics of the C2 and factor B genes

This review summarises our current knowledge of the genetic organisation, structure and polymorphism of the loci for the complement proteins, C2 and Factor B--class III gene products of the major histocompatibility complex. cDNA probes specific for C2 and Factor B have been used to screen cosmid libraries of human genomic DNA, and this has allowed isolation and characterisation of the corresponding genes. Southern blot analysis of the cosmid clones and of uncloned genomic DNA has shown that there are single C2 and Factor B loci that are less than 500 bp apart. Molecular mapping has revealed that the C2 gene spans approximately 18 kb of DNA. This is in marked contrast to the Factor B gene which is 6 kb in length. The entire gene structure of the Factor B gene has been determined and the interesting features of this gene which have emerged from an examination of the intron-exon boundaries are discussed. C2 and Factor B are polymorphic and structural variants have been detected by differences in charge. The degree of polymorphism at the C2 and Factor B loci has been examined by Southern blot analysis of restriction digests of genomic DNA. Three DNA polymorphisms have been identified in the C2 gene. These polymorphisms subdivide the common allelic variant of C2 (C2C) and reveal that there is much greater variability at the C2 locus than that detected by protein typing. It is suggested that these DNA polymorphisms may serve as useful markers in the genetic analysis of diseases that are related to the major histocompatibility complex.

DNA polymorphism of the C2 and factor B genes. Detection of a restriction fragment length polymorphism which subdivides haplotypes carrying the C2C and factor B F alleles

Factor B and the second component of complement (C2) in man are encoded within the major histocompatibility complex by single loci that are less than 1 kb apart. A 2.3 kb factor B-specific cDNA probe has been used to examine, by Southern blot analysis, the genomic DNA of individuals typed for C2 and factor B by protein electrophoresis. We have identified a restriction fragment length polymorphism using the endonuclease Taq I, which subdivides haplotypes carrying both the common variant of C2 (C2C) and the fast (F) variant of factor B. This DNA polymorphism has been mapped to lie in the C2 gene and represents a new genetic marker not defined by protein electrophoresis. This polymorphism may serve as a useful marker in the genetic analysis of diseases that are related to the major histocompatibility complex.

Complement and cancer: activation of the alternative pathway as a theoretical base for immunotherapy

Activation of the APC is pointed out as the common factor in all sufficiently studied cancer treatments employing nonspecific, active immunotherapy. This chapter outlines the molecular biology of both APC and classical pathway of complement, summarizes the alternative pathway's biologic activities especially in relation to the C3/C5 convertase C3b,Bb, and its implications in the mechanism of host defense against malignancies, particularly relating to the activated macrophage. The many involvements of the APC in the various agents used for nonspecific active immunotherapy are reviewed, and possible clinical implications outlined. It is concluded that activation of the APC can be proposed as the specific theoretical basis so far lacking for this treatment modality and that it is accordingly feasible to attempt to monitor clinical application of this principle by fine-tuning of APC activation in cases of human cancer.