Mouse IgG1 Lambda Isotype Control Antibody [APC/CY5.5]

This investigation describes the detection of a component in Escherichia coli capable of binding a large proportion of human antibody variable domains including otherwise highly monospecific antibodies induced by an in vivo antibody response. This interaction is of low affinity, but cross-linking of IgG molecules by, e.g. anti-immunoglobulin preparations, provides a sufficient degree of multivalency to promote a high avidity interaction. This binding which occurs both with kappa and lambda light chain-containing antibodies, appears to involve the variable region of human antibodies making it a superantigen-like activity. This is proposed based on the facts that: (i) different human antibodies of IgG1 isotype appear to bind to different extents suggesting that variable domain differences determine the binding activity; and (ii) addition of soluble antigen abrogates the interaction with the E. coli-derived molecule. Future studies of the nature and possible in vivo consequences of these interactions are warranted since any superantigen activity associated with this binding might affect the human immune response occurring as a consequence of E. coli infections.

Antibodies binding to double-stranded (ds) DNA are strongly associated with renal involvement in patients with systemic lupus erythematosus (SLE). We have generated two new IgG DNA-binding monoclonal antibodies (mAb), RH-14 and DIL-6, from the peripheral blood lymphocytes of two SLE patients with glomerulonephritis using the heteromyeloma cell line CB-F7. RH-14 is an IgG1 lambda antibody which also bound to single-stranded DNA, histones and nucleosomes. DIL-6 is an IgG3 lambda antibody with restricted antigen binding specificity. cDNA encoding the variable regions of the heavy (V-H) and light (V-L) chains of RH-14 was sequenced and the antigen binding site of this mAb was computer modelled. Sequence analysis of V, and V-L regions of RH-14 showed that V-H is derived from germ-line gene V3-7, a member of the V(H)3 family, and V-L is derived from DPL 11, a member of the V(lambda)2 family. Somatic mutations and basic amino acid residues are identified in the complementarity-determining regions of both V-H and V-L regions. The nephritogenic properties of these mAb were analyzed by implanting and growing the hybridoma cells secreting the mAb in the peritoneum of SCID mice. The animals that received the RH-14 hybridoma produced higher levels of proteinuria (3 to greater than or equal to 4) (p < 0.001) compared to the groups that received DIL-6 (trace to greater than or equal to 1) or CB-F7 (trace). Electron microscopy of kidney sections from all the RH-14-implanted animals showed granular immunoglobulin deposition in the renal glomerular capillaries and mesangium. in this study we have shown for the first time using electron microscopy that a human IgG anti-dsDNA mAb, RH-14, is nephritogenic and that deposition of such an antibody alone is sufficient to induce renal damage.