Our results show that the guinea pig tTG ELISA is suitable for use as a simple diagnostic screening and follow-up method for GSE. Further studies are necessary to identify possible additional minor antigens in GSE.

We confirmed the findings of Ey and colleagues that mouse IgG is absorbed by protein A-Sepharose at pH 8.0. Also confirmed was their finding that IgG1 mainly elutes from such a column by means of a buffer with pH 6.0 and that the corresponding pH values for IgG2a and IgG2b were 4.5 and 3.5. We made the new finding that the bulk of IgG2a bearing allotypes a or j eluted already at pH 5, in contrast to IgG2a bearing allotype b. Another new finding was that IgG3 was mainly eluted at pH 4.5 regardless of the allotype. All four subclasses of IgG could thus be physically separated if the allotype was a or j (the only known exception is allotype b). Separation of IgG2a and IgG3 was achieved even when the allotype was b by using a pH gradient for elution. IgG2a came out at a slightly higher pH than IgG3. Mouse IgG antibodies against group A streptococcal polysaccharide belonged mostly to IgG3 and, to a lesser extent, to IgG2a and IgG2b.

Mice were immunized with alpha (1-6) dextran, either as such or coupled to protein carriers, and their anti-dextran response was measured by a solid-phase radioimmunoassay and the Farr assay. Like earlier investigators we found that protein-conjugated dextran was more antigenic than plain dextran. Our novel findings were that (1) a standard dose (30 micrograms of dextran per injection) coupled to strongly antigenic protein (chicken serum albumin (CSA) was three times more antigenic than dextran coupled to weakly antigenic bovine serum albumin (BSA); (2) dextrans of low molecular weight (1000-10,000 daltons) coupled to CSA induced at least ten times stronger secondary responses than did a similarly coupled macromolecular dextran (5-40 million daltons); (3) variation of the CHO/protein ratio from 0.3 to 1 had little effect on the antigenicity of the dextran. Increase of the ratio from one appeared to decrease immunogenicity when BSA was the carrier but not when CSA was the carrier.

Humoral immune responses are traditionally characterized by determining the presence and quality of Abs specific for certain Ags. Arraying of large numbers of Ags allows the parallel measurement of Abs, generating patterns called Ab profiles. Functional characterization of these Abs could help draw an even more informative map of an immune response. To generate functional Ab profiles we simultaneously tested not only IgM, IgG, and IgA binding to, but also complement activation by, a panel of endogenous and exogenous Ags printed as microarrays, using normal and autoimmune human sera. We show that complement activation by a particular Ag in a given individual cannot be predicted by the measurement of Ag-specific Abs, despite a general correlation between the amount of Ag-bound Ab and the deposited C3 fragments. This is due to both differences in the isotypes that dominate in the recognition of an Ag and individual variations for a given isotype, resulting in altered complement activation potential. Thus, Ag-specific C3 deposition can be used as an additional parameter in immune response monitoring. This is exemplified by comparing the coordinates of Ags, used for the diagnosis of systemic lupus erythematosus, of normal and autoimmune serum samples in a two-dimensional space derived from C3 deposition and Ab binding. Since cleavage fragments of C3 mediate important immunological processes, we propose that measurement of their deposition on Ag microarrays, in addition to Ab profiling, can provide useful functional signature about the tested serum.