Isotypes of antibodies induced by plain dextran or a dextran‐protein conjugate

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Abstract
Mice were immunized with a(1→6) dextran or its protein conjugate with monthly intervals, and their antibodies were quantitated with an isotype-resolved radioimmunoassay. Plain dextran (molecular weight = 5–40 million) induced antibody concentrations varying from 20 to 80 μg/ml (primary response). The resposse to a booster injection was weaker than the response to the first injection. More than 90% of anti-dextran antibodies were IgM but IgG and IgA responses could be unequivocally demonstrated. IgG1 and IgG3 were the predominant subclasses of IgG. Dextran antibody responses to a conjugate of dextran (molecular weight ≈ 10 000) and chicken serum albumin (CSA) were stronger (80–300 μg/ml) than responses to plain dextran, and anti-CSA responses to the conjugate were even stronger (up to 900 μg/ml). Three distinctly different isotype patterns were observed. A pattern IgM ≫ IgG1 = IgG3 > IgG2a prevailed in responses to the plain dextran and in primary anti-dextran responses to dextran-CSA. Another pattern IgG1 > IgG3 > IgM > IgG2a was observed in late anti-dextran responses to dextran-CSA. The third pattern IgG1 ≫ IgG2a > IgG3 ≈ IgM was characteristic of anti-CSA antibodies. Little IgG2b or IgA antibodies were found. Different isotype patterns can best be explained on the basis of secondary factors such as T cell help.

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