Significance of the third hypervariable region of the antibody heavy (H) chain for antigen-specificity and expression of idiotypes during the thymus-dependent immune response
Antigen receptors of B lymphocytes are membrane-bound antibodies. Their binding-site is created by the combined action of variable (V) domains of heavy (H) and light (L) chains. VH is encoded by variable genes and diversity-enhancing (D) and joining (J) gene segments while VL is encoded by VL genes and J segments only. The V(D)J recombinatorial genetic reper¬toire is in the range of 107. In addition, a much larger non-genetic repertoire is created by im¬precise recombination around the D gene segment. In the present communication, the immune response to the hapten-carrier complex 2-phenyl-oxazolone coupled to chicken serum albu¬min as a model antigen was investigated in 2 BALB/c mutant mouse strains. Instead of 13 D gene segments as in wildtype, these mice harbour only 1 D segment in their genome coding preferably for hydrophobic or charged amino acids, respectively. In comparison to wildtype mice, both mutant strains exhibited T cell defects since their IgM>IgG class switch recombi¬nation and immune maturation was impaired and clonal development appeared to be deregu¬lated.
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