Mixed-Lymphocyte Reaction

By Levi Clancy for Student Reader on

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The mixed-lymphocyte reaction (aka the mixed-leukocyte reaction, or MLR) is an in vitro method for assaying CD4 (aka TH) cell proliferation and for generating a population of CD8 cells (aka cytotoxic T lymphocytes, or CTLs).

When allogeneic (different MHC haplotype) lymphocytes are cultured together, CD4 (aka TH) cell populations expand. Within another 48 hours, an expanding CD8 cell (aka CTL) population is generated. CD4 (TH) cells, dendritic cells and certain accessory cell types are all critical for the MLR to function.

The total proliferation of lymphocytes from the allogeneic strains is measured by adding [3H]-thymidine to the culture medium and monitoring its uptake (uptake occurs during each cell division).

However, it is unclear from [3H]-thymidine uptake how much each individual population has proliferated. The one-way mixed-lymphocyte reaction (aka the one-way mixed-leukocyte reaction or one-way MLR) resolved this issue.

One population -- the stimulator -- is first inactivated (via mitomycin c or lethal x-irradiation) before being added to the MLR well. These inactivated cells merely provide foreign alloantigens to the responder population.

Within 24-48 hours, the responder T cells have begun proliferating and within another 48 hours an expanding population of functional CTLs has been formed.