The biological half-lives of four rat immunoglobulin isotypes.

Purified preparations of monoclonal rat IgG2a, IgG1, IgM and monomeric IgA, and of polyclonal IgG, were lightly radiolabelled with 125I and injected intravenously into rats. Blood samples were taken so that the half-life of each immunoglobulin isotype could be calculated. Half-life was defined as the time taken for the specific radioactivity present in the blood 24 h after injection to fall by half. The half-life values thus obtained were 106 h for IgG2a, 53 h for IgG1, 63 h for polyclonal IgG, 25 h for IgM and 27 h for monomeric IgA.