Mitogenic Activation of Human Lymphocytes: a Protein A Plaque Assay Evaluation of Polyclonal B-Cell Activators

Using the protein A plaque assay, the capacity of various polyclonal B cell activators to induce differentiation in human B lymphocytes was investigated. Dextran sulphate and native Dextran were both virtually devoid of mitogenic properties, Lipopolysaccharide, however, was round to be a potent mitogen in human cells that, although giving rise to low DNA synthetic response, induced high numbers of immunoglobulin-synthesizing cells. Mean plaque-forming cell (PFC) numbers in healthy blood donors assayed on the optimal day (days 5–7) were 23, 493 IgM/10⁴ cells, 11, 288 IgG/10⁶ cells, and 2643 IgA/10⁶ cells. Values obtained in spleen cells, peaking at days 4–6, were slightly higher. Purified protein derivative (PPD) was equally or oven more-effective than lipopolysaccharide (LPS) in generating PFC of different subclasses in peripheral blood with mean of 29, 241 IgM/10⁶, 21, 269 IgG/10⁶, and 3681 IgA/10⁶. PPD furthermore induced a marked DNA synthetic response in human lymphocytes. These data suggest that LPS and PPD may both be used as functional markers in human cells when analysing patients with a suspected immunodeficiency state. It is suggested that cultures should be assayed using the protein A plaque assay, thereby being able not only to investigate the individual immunoglobulin classes but also to avoid the possible hazards involved in measuring antigen-specific responses in patients whose prior immunization to the antigen tested can never be totally excluded