Complementarity-determining regions (CDRs) in B and T cell receptors interact with antigens, determining specificity. These hypervariable regions in the receptor's variable domains play a crucial role in antigen recognition. Diverse receptor repertoires are achieved through V(D)J recombination, junctional diversity, N region addition, combinatorial diversity, gene conversion, and somatic hypermutation, ensuring recognition of various antigens.

The human and mouse immune systems have different counts of V, D, and J gene segments for B and T cell receptors. Mice generally have a larger repertoire of V gene segments, compensating for fewer D and J gene segments in some cases. Both species achieve diverse BCR and TCR repertoires through V(D)J recombination.

B-cell receptors (BCRs) on B lymphocytes recognize antigens, initiating the immune response. They consist of heavy and light chains with variable and constant domains. BCRs associate with CD79a and CD79b, which activate B cells upon antigen binding. Multiple BCRs can bind antigens and activate B cells. BCRs play a crucial role in immune response.