Immunoglobulin Quantitation and Enumeration of Immunoglobulin-producing Cells: Comparison of Two Indexes of B-Cell Activation

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Abstract
Human lymphocytes were cultured under different conditions to determine the effects of technical variations on the response to pokeweed mitogen (PWM) and Staphylococcus aureus as measured by quantitation of Ig in the culture supernatants and enumeration of Ig-secreting cells (ISC) by a reverse plaque technique. The highest numbers of ISC were measured when the cells were cultivated in standing tubes, without glutamine supplementation during the culture and at a concentration of 1 .times. 106 cells/ml. The highest Ig concentrations were measured under similar conditions, except that somewhat higher values were obtained with cells cultivated at 1 .times. 106/ml in 2 ml cultures with PWM stimulation and at 2.5 .times. 106/ml in 1 ml cultures with S. aureus stimulation. In time-course studies, peak ISC responses occurred on day 5 with each mitogen; extracellular Ig levels kept rising until day 7, possibly owing to accumulation of secreted Ig. Measurements of the numbers of ISC and of secreted Ig levels in simultaneous cultures of lymphocytes from the same donors showed no correlation; co-stimulation of cultures with PWM and concanavalin A (to stimulate suppressor cells) depressed Ig levels and ISC numbers. Heterogeneity in the plaque-forming cell population with respect to rate of Ig secretion is suggested. Apparently, these 2 techniques both reflect B cell activation. They should not be considered interchangeable; the two should probably be used in conjunction for complete characterization of B cell activation.