Based on the fact that there is a shift in lymphocyte populations in the inflammatory infiltrate from predominant T cells in gingivitis to an increased proportion of B cells in periodontitis, some authors suggest that the susceptibility to periodontal disease progression may involve predominantly Th2 cells which produce the cytokines required for B-cell proliferation and differentiation, leading to polyclonal B-cell activation, the production of elevated levels of nonprotective antibodies, and the continued production of B-cell IL-1. This evidence concerns the gene IL1A and periodontitis.