Biological activity of complement fragment Ba

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Ba is one of the fragments of complement proteins that is generated upon activation of complement system. Ba is cleaved from factor B by factor D that belongs to the altemative pathway of complement system. Recently, the biological effects on the lymphocytes and macrophages have been reported in the Ba fragment of factor B.However the further investigation of the biological functions of Ba has been hampered mainly by the difficulty in purifying Ba in a large amount that needs many Purified complement proteins and very much complicated purifilcation steps. We intended to circumvent this laborious procedures by making recombinant Ba fragment.A full-length cDNA for factor B was isolated from the human liver cDNA library. As Ba (234 amino acid residues) corresponds to the amino terminal one third of factor B,we introduced a stop codon at the 235th amino acid residue by using site-directed mutagenesis. The mutant factor B cDNA coding for Ba fragment was trnsfected and expressed in CHO cells. The culture media containing has been subjected to the purification of recombinant Ba by using an affinity column.The association of deficiencies in the complement proteins and bacterial/viral infections and autoimmune diseases has been implicated. The molecular defects leading to the complement deficiencies has not been studied in detail. We studied the molecular bases for C6, C7, C8 and C9 deficiencies that are important in the activation of factor B.We first identified the genetic abnormalities in the deficiencies of C6 and C7. A two kinds of homozygous lbp deletion were shown in two patients with C6 deficiency, while a nonsense mutation and a 2bp deletion were identified in two patients with C7 deficiency, respectively. We have shown a nonense mutation at Arg-95 was predominant in Japanese C9 deciciency.