Cautions

There is no clinical utility to assessing antigen responses in infants younger than 3 months due to limited antigen exposure and vaccination. The only exception would be infants who develop candidiasis prior to 3 months of age.

When interpreting results, note that the range of lymphocyte proliferative responses observed in healthy, immunologically competent individuals is large. The reference ranges provided will be helpful in ascertaining the magnitude of the normal response.

Lymphocyte proliferation to mitogens is known to be affected by concomitant use of steroids, immunosuppressive agents, including cyclosporine, tacrolimus (FK506), Cellcept (mycophenolate mofetil), immunomodulatory agents, alcohol, and physiological and social stress.

Lymphocyte proliferation responses to antigens (and mitogens) are significantly affected by time elapsed since blood collection. Results have been shown to be variable for specimens assessed between 24- and 48-hours post blood collection. Therefore, lymphocyte proliferation results must be interpreted with due caution and results should be correlated with clinical context. Specimens more than 24-hours old may yield spurious results.

Diminished results may be obtained in cultures that contain excess neutrophils or nonviable cells.(7)

Timing, and consistency in timing, of blood collection is critical when serially monitoring patients' lymphocyte subsets (specifically T cells in this context) and their diurnal variation can potentially affect the magnitude of the proliferative response, especially in patients who already have severe T-cell lymphopenia. The absolute counts of lymphocyte subsets are known to be influenced by a variety of biological factors including hormones, the environment, and temperature. The studies on diurnal (circadian) variation in lymphocyte counts have demonstrated progressive increase in CD4 T-cell count throughout the day, while CD8 T cells and CD19+ B cells increase between 8:30 a.m. and noon, with no change between noon and afternoon. Natural killer-cell counts, on the other hand, are constant throughout the day. Circadian variations in circulating T-cell counts negatively correlate with plasma cortisol concentration. In fact, cortisol and catecholamine concentrations control distribution and, therefore, numbers of naive versus effector CD4 and CD8 T cells. It is generally accepted that lower CD4 T-cell counts are seen in the morning compared with the evening(8) and during summer compared to winter.(9)