Selective expression of the interleukin-2 gene discriminates between the auto- and allo-mixed lymphocyte reaction.

The in vitro mixed lymphocyte reaction (MLR) is a useful model to study alloresponsiveness to histocompatibility antigens. Secretion of different cytokine proteins in the supernatant of allo-MLR cultures has been reported in a few studies with no reference to results in auto-MLR. Since most cytokines are autocrine factors, their levels in the supernatant may not reflect the actual intracellular production. Therefore, we studied cytokine gene expression in auto- and allo-MLR by Northern dot blotting and reverse transcriptase-polymerase chain reaction (RT-PCR) analysis. mRNA for IL-beta and IL-8 was detected in both auto- and allo-MLR by Northern dot blotting. mRNA for IL-2, gamma-IFN, TNF-alpha, IL-4, IL-10 and IL-2 receptor (IL-2R) was not found by Northern dot blotting and could only be detected by RT-PCR. Expression of mRNA for IL-4, IL-10, TNF-alpha, gamma-IFN and IL-2R by RT-PCR analysis was seen in both auto- and allo-MLR. There was slightly increased expression of gamma-IFN, IL-2R and TNF-alpha in allo-MLR in comparison to auto-MLR. However, IL-2 was exclusively expressed in allo-MLR and was detected as early as 5 h of initiation of culture. These results indicate that mRNA expression for a number of cytokines can be seen in both auto- and allo-MLR using RT-PCR analysis. However, the consistent expression of IL-2 in the allo-MLR indicates that it is an important cytokine which discriminates an allo- from an autoresponse. These findings suggest that detection of IL-2 gene expression by RT-PCR may be useful for immune monitoring of allograft rejection.