IGHE and neoplasm: A strong isotype-switched anti-tumor antibody response was produced in response to cognate CD4+ T cell help, with large increases in the serum levels of IgG1, IgG2c (the functional equivalent of IgG2a, which is not present in C57BL/6 mice [30]) and IgG2b, and smaller increases in IgG3, IgA and IgE (Figure 5C and 5D).