Faculty Bibliography

Protein WIS is a human gamma3 heavy (H) chain disease immunoglobulin variant whose amino acid sequence is most readily interpreted by postulating that three residues of the amino terminus are followed by a deletion of most of the variable (VH) domain, which ends at the variable-constant (VC) joining region. Then there is a stretch of eight residues, three of which are unusual, while the other five have striking homology to the VC junction sequence. This is followed by a second deletion, which ends at the beginning of the quadruplicated hinge region. These findings are consistent with mutations resulting in deletions of most of the gene coding for the V region and CH1 domain followed by splicing at the VC joining region and at the hinge. These structural features fit well the notion of genetic discontinuity between V and C genes and also suggest similar mechanisms of excision and splicing in the interdomain regions of the C gene of the heavy chain.

Amino acid sequence analysis of the pFc' fragment obtained by pepsin digestion of a human IgG2 myeloma protein PIG Gm (n or 23) negative shows it to consist of 112 residues. It starts at position 334 (gamma1 numbering) and contains eight residues from the Cgamma2 region, and the whole Cgamma3 domain. Comparison with the sequence of gamma1 shows two differences at positions 339 and 397. Each of them can be explained by a single base substitution. This high degree of homology among gamma-chain subclasses suggests a recent diversification.

Amino acid sequence studies of the amino terminal 25 residues of amyloid A (AA) protein and the serum precursor (SAA) induced with casein or LPS indicate differences in the sequence at position 6 and significant heterogeneity at several other positions in SAA. These findings suggest that SAA is a polymorphic serum protein and raise the possibility that only certain forms of SAA are processed to the tissue amyloid fibril.

A unique case of gamma3 heavy chain disease with two related serum proteins is reported. One molecule appears to be an IgG3lambda myeloma protein. The second molecule is a dimer of a shortened gamma3 heavy chain that has an unblocked amino terminus and lacks the VH and CH1 domains. Its probable origin as a synthetic product is discussed. The clinical and pathologic features of this patient resemble those of other patients with gamma heavy chain disease more than those of patients with multiple myeloma. It seems likely that the heavy chain disease protein is the result of a mutational event in the malignant clone originally producing the myeloma protein.