Cellular immune defect in selective IgA deficiency using a microculture method for PHA stimulation and limiting dilution

Abstract

Ten children with selective IgA deficiency were evaluated for cell-mediated immunity (CMI) which included a micromethod for phytohemagglutinin (PHA) stimulation. Standard tests for CMI including the macromethod (400,000 cells) for PHA stimulation were all normal in these patients. However, with the micromethod (2500 cells), the response to PHA of lymphocytes from patients with selective IgA deficiency was significantly depressed ( P = 0.03). Limiting dilution was performed by culturing 400 to 2500 cells with PHA. In five patients there was a significant decrease in the absolute response to PHA at each cell number ( P = 0.02). In this group there was also a diminished slope of the linear regression curves, suggesting that in some patients with selective IgA deficiency the defect in CMI may result from a decrease in the efficiency of T lymphocytes to respond to PHA. To evaluate the mechanism for the increased sensitivity of the micromethod, we did cell counting experiments. We found that while the macromethod resulted in no increase in cell number on the day of peak DNA synthesis, there was a six- to seven-fold increase in cell number in the microcultures indicating that the cell response to PHA in the microcultures is to undergo multiple cell divisions. The enhanced sensitivity of the micromethod may be due to: (i) magnification of a defect in any single cell by 2 N when N is the number of generations that cell will make in culture; and (ii) the diluting out of cell populations which may be limiting to the overall response.