The singularity of IGHV4-34 links infection, autoimmunity, and B-cell tumors

B cells expressing the IGHV4-34 gene sit at the centre of a web of B-cell functions, ranging from natural antibodies induced by infection through to autoimmunity and tumors. Tracking via the 9G4 monoclonal antibody (MoAb) specifically directed against the unique flag sequences in the first framework region (FR1) of IGHV4-34, allows insight into the evolving nature and multiple functions of B cells expressing a single IGHV gene. IGHV4-34+ B cells are found early in development, and expansion indicative of a superantigenic drive occurs with increasing age. IGHV4-34+ B cells secrete IgM in various hematologic conditions, including the mandatory association with cold agglutinins, and transient expansions of usage (not always overt agglutination) are seen in EBV, CMV, Mycoplasma pneumoniae and other infections. Perhaps connected to that, certain autoimmune conditions, such as systemic lupus erythematosus, show increases in IGHV4-34 expression which correlate with disease flares. Intriguingly there is preferential usage of IGHV4-34 in a wide range of lymphomas and in the IgG variant of chronic lymphocytic leukemia, suggestive of an autoantigenic drive. Structurally, both the interaction of the 9G4 MoAb, and the ability of the IGHV4-34-encoded protein to bind to N-acetyl lactosamine-containing sequences, rely on hydrophobic amino acids located in two positions of the looped FR1 sequence of the variable domain. This offers a focused site for blockade. IGHV4-34 is a paradigm of the plasticity of B cells, of interaction with potential autoantigens, and of their subversion in tumors.