Influence of molecular size of IgA on its immunoassay by various techniques--I. Direct and reversed single radial immunodiffusion.

Immunochemically pure samples of monoclonal and polyclonal IgA were prepared from human sera and milk. Samples of various homogeneous molecular sizes were further obtained by preparative ultracentrifugations. The different behaviour of each preparation (monomer, dimer, trimer, tetramer and secretory IgA) were studied in direct (DRID) and reversed (RRID) single radial immunodiffusion using three different anti-alpha-chain antisera and IgA samples of various monoclonal and polyclonal origins. In DRID, all polymer concentrations were underestimated when using monomers as standards, on an equal weight (OD) basis. Correction factors (CFs) were calculated from monomer to polymer DRID slope ratios. The means +/- SDs of these CFs were 1.55 +/- 0.18 for serum dimers, 1.85 +/- 0.10 for trimers, 2.63 +/- 0.26 for tetramers and 2.24 +/- 0.15 for secretory IgA (84% 11S, 16% 15S). These results were confirmed by RRID.

Rat monoclonal antibodies. VI. Production of IgA secreting hybridomas with specificity for the 2,4-dinitrophenyl (DNP) hapten.

A simple method to obtain rat hybridomas producing specific IgA antibodies is reported. By fusing the IR983F rat myeloma cell line with mesenteric lymph node cells from LOU/C rats immunized via the Peyer's patches with DNP-Salmonella typhimurium, twenty hybrids secreting monoclonal IgA antibodies specific for DNP were produced and maintained as highly secreting transplantable ascitic tumors. The monoclonal IgA antibodies were easily purified by affinity chromatography on a DNP-immunosorbent and were found to comprise both monomers and polymers.

In vivo experiments involving secretory component in the rat hepatic transfer of polymeric IgA from blood into bile.

Human or rat purified secretory IgA (sIgA) injected intravenously (i.v.) into rats is transferred to bile much less (seven to twenty-four times) than human or rat polymeric IgA (pIgA) devoid of secretory component (SC). A polymeric Fc alpha (pFc alpha) fragment of a human IgAl myeloma protein, obtained by IgA-protease digestion, bound in vitro to rat SC and was actively transferred in vivo into bile, in contrast to the corresponding Fab alpha. The IgA recovered in bile was not degraded, as judged by sedimentation in density gradients. Purified rabbit IgG anti-rat SC antibody was also efficiently transported in vivo into bile, about forty times more than normal rabbit IgG. The biliary transport of anti-Sc antibody could be reduced and retarded by the simultaneous i.v. injection of purified rat SC or human pIgA. The transfer of rat 125I-pIgA into bile was also significantly reduced and retarded by the concomitant i.v. injection of purified rat or human SC. Moreover, i.v. injection of purified rat or human SC induced a marked and prolonged decrease of the sIgA level in the bile. Rat SC was more effective than human SC in this respect. All these in vivo experiments confirm the in vitro findings of Orlans, Peppard, Fry, Hinton : Mullock, (1979) and Socken, Jeejeebhoy, Bazin & Underdown, (1979) showing that Sc is the IgA-receptor on the hepatocyte membrane for the transfer of pIgA from rat plasma into bile.