Final answer:
The M component in a monoclonal gammopathy refers to an abnormal protein found in the blood. In the case of MGUS or multiple myeloma, the M component is typically an excessive amount of IgM antibody, which is a pentamer formed by plasma cells.
Step-by-step explanation:
Monoclonal gammopathy refers to the presence of a single abnormal protein in the blood. The M component, also known as the monoclonal component, is the abnormal protein found in monoclonal gammopathy. In the case of monoclonal gammopathy of undetermined significance (MGUS) or multiple myeloma, the M component is usually an excessive amount of a specific type of immunoglobulin, known as IgM antibody. IgM antibody is a pentamer, meaning it consists of five individual IgM molecules bound together by a protein structure called the J chain. These pentamers are produced by plasma cells, which are antibody-secreting cells.