Interferon-gamma plays a key role in the human mixed lymphocyte culture

Measurement of cytokines in the mixed lymphocyte culture (MLC) is thought to be a new and relevant parameter for bone marrow transplantation (BMT). Our experiments showed that IFN-gamma plays a central role in the cytokine network following alloantigenic recognition. IFN-gamma itself is induced by IL-2 since anti-IL-2 strongly reduced the secretion of IFN-gamma. As anti-IFN-gamma also diminished the response of IL-2 and sIL-2R, a feedback mechanism between these two cytokines is assumed. Addition of rIFN-gamma to the MLC augmented the release of sCD8 molecules, whereas sCD4 molecules were reduced, indicating that IFN-gamma led to T cell differentiation instead of IL-2 dependent proliferation. In the MLC, a feedback mechanism between TNF-alpha and IFN-gamma exists, since anti-TNF-gamma reduced the secretion of IFN-gamma and anti-IFN-gamma inhibited the release of TNF-alpha. Therefore, IFN-gamma plays a critical role in monocyte activation, T cell differentiation, and IL-2-induced cell growth. We conclude that measurement of IFN-gamma might be a new and more sensitive parameter for BMT than the established proliferation assay, since IFN-gamma directly quantifies T cell activation.

[Cytokines in mixed lymphocyte culture as a prospective parameter for transplantation]

BACKGROUND

The human mixed lymphocyte culture (MLC) is an important model for allogeneic recognition established in the clinical routine of bone marrow transplantation (BMT). The measurement of proliferation in the MLC has no high predictive value either for the rejection nor for the graft-versus-host-disease and may not be used for the transplantation of cadaveric allografts because of its long duration.

METHOD

Since cytokines in the MLC represent more specific parameters, a two-way MLC measuring cytokine release on protein level was developed. In this system, IFN-gamma played a key role inducing the cytotoxic reaction, the monocyte activation and the IL-2-induced cell proliferation.

RESULT

Further, a reverse transcription polymerase chain reaction (RT-PCR) in the MLC was established that detects mRNA of a broad panel of cytokines (IL-1 beta, IL-2, IL-4, IL-6, IL-9, IL-10, TNF-alpha, TNF-beta, IFN-gamma, TGF-beta).

CONCLUSION

The expression of mRNA allows to evaluate the cellular-mediated and the humoral-mediated immune response as well as the endogenous suppression between recipient and donor in a prospective manner. Since this method takes only several hours, it may be suitable not only for BMT but also for the transplantation of cadaveric allografts. In conclusion, cytokine-MLC by RT-PCR might be an important step for prospective testing of immunological compatibility in transplantation medicine.

Identification of HLA-DRB1 and HLA-DQB1 identical individuals by a cytokine-based mixed lymphocyte culture

Cytokine determination in MLC is under discussion as providing more sensitive and specific information regarding host-graft compatibility, and is therefore suggested to represent a new method for transplantation medicine. Little is known, however, about the stimulatory influence of HLA class II antigens and minor lymphocyte-stimulating antigens (Mls). Our results demonstrate that cytokine determination in MLC is suitable to detect identical alleles of HLA-DRB1 and HLA-DQB1. Among more than 100 random MLC experiments, we observed one cytokine pattern similar to the cytokine release detected in a control MLC of HLA-identical siblings, which showed marginal or no secretion of IL-2, sIL-2R, IFN-gamma, TNF-alpha, and IL-6. HLA-typing of these two nonreactive individuals elevated identical HLA-DRB1 and HLA-DQB1 regions, while they differed in the HLA-DP locus. This suggests that HLA-DP has no stimulatory influence on cytokine release. Further investigation of the stimulatory capacity of HLA-DR and DQ showed that HLA-DR is more effective in inducing IFN-gamma release than HLA-DQ. To evaluate the stimulatory influence of human Mls, i.e., human endogenous retroviruses (HERV), we analyzed HERV sequences of nonreactive individuals. Both individuals showed identical HERV patterns. A third individual, who had shown distinct cytokine release in MLC with both nonreactive individuals, differed in the HERV fragments. In conclusion, cytokine determination in MLC is a new method of evaluating the biological relevance of stimulatory antigens after allogeneic stimulation detecting all individual diversities in one experiment.

Cytokine interactions in human mixed lymphocyte culture

Human PBMC of healthy blood donors were used to investigate the interaction of cytokines in human MLC. Two-way MLC was performed because irradiation did not influence the cytokine release. We found different kinetic patterns for IL-2, IFN-gamma, and sIL-2R. Production of IFN-gamma was dependent on IL-2 release because anti-IL-2 addition resulted in more than 90% reduced IFN-gamma levels. Treatment with rIL-2 altered IFN-gamma kinetics, but not the total amount of IFN-gamma. Addition of anti-IFN-gamma led to decreased production of IL-2 and sIL-2R. A down-regulation of IL-2 and sIL-2R could also be observed after treatment with rIFN-gamma. No production of IL-4 and IL-10 was detected in MLC (detection limit 5 pg/ml). This could not be explained by IFN-gamma antagonism because IL-4 and IL-10 were not detectable even after addition of anti-IFN-gamma. Testing the TH1-TH2 cell antagonism, the addition of rIL-4 and rIL-10 resulted in IFN-gamma suppression depending on the timing of exposition. Treatment with rIL-10 inhibited IL-2 and sIL-2R release. We found no production of IL-1 alpha and IL-1 beta in MLC, whereas IL-6 and TNF-alpha release could be detected. Surprisingly, release of IL-6 and TNF-alpha could be blocked completely by addition of anti-IFN-gamma. This suggests that the release of IL-6 and TNF-alpha in MLC is dependent on IFN-gamma produced by T cells. In summary, TH1 cytokines play a central role in MLC regulation, whereas TH2 cytokines appear to be of little importance.