The early immune response tends to produce polyspecific antibodies, i.e. antibodies that recognize various epitopes and IgM antibodies are a classical example. However, during affinity maturation lymphocytes are progressively antigen-educated and the specificity of mutated antibodies to a foreign protein dramatically improves.
I would be interested to understand what we know about the expression of proteins or surrogate markers on B lymphocytes that would tell us something about the state of maturity.
A model antigen NP is used in conjugation with an adjuvant like CGG or ficoll to induce a specific immune response and affinity mature antibody can be detected in germinal center cells from spleen using a FACS antibody that can detect the cell surface Ab expressed by B cells specific to NP. ELISA can also be done to detect low or high affinity NP antibody in serum. In terms of other B cell markers: B cells in spleen are usually naive in SPF facility where mice are kept usually. These cells express IgM on their surface and are CD43 -ve and B220+. GC B cells express CD95, GL7 and PNA, all of which are surface markers detectable by flow cytometry. Good-luck
IgM reactive with any antigen will always have the same low affinity, but a high avidity due to fact that it is a pentamer with 10 AGB sites. There is no memory or affinity maturation for IgM. As far as I know IgD, IgE, IgA, also lack memory or affinity maturation. To find sequentially occuring lymphocytic membrane or cytoplasmic markers correlating with an increasing degree of affinity maturation could be possible by harvesting spleen cells of inbred mice at different time intervals after the start of an immunization with a simple, easy to essay antigen. The drawback of high affinity IgG is that it starts to interact with other look-alike epitopes than the epitopes of the antigen used for immunization.
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