MyD88 (Myeloid differentiation primary response gene 88) is a protein that is encoded by the MYD88 gene in humans. Available evidence suggests that MYD88 is dispensable for human resistance to common viral infections and to all but a few pyogenic bacterial infections, demonstrating a major difference between mouse and human immune responses. MyD88 is an essential adaptor protein in the IL-1R1 signaling pathway. MyD88 may define a family of signal transduction molecules with an ancestral function in the activation of the immune system. MyD88 functions as a pure adaptor linking the IL-1R1 to downstream IRAK kinases. Mutation in MYD88 at position 265 leading to a change from leucine to proline have been identified in many human lymphomas including ABC subtype of Diffuse Large B-cell Lymphoma and Waldenstrom's Macroglobulinemia.