<prompt> Mixed lymphocyte culture is used to indentify :MHC class I antigen.MHC class II antigen.B lymphocytes.T helper cells.  <response>: Ans. is b i.e. MHC class II antigen Mixed lymphocyte culture is used to identify HLAIIHarrison says - HLAII genes were first detected by their ability to stimulate lymphocyte proliferation by mixed lymphocyte reaction.Some more information about Major histocompatibility complex:Human Major histocompatibility complex commonly called the human leucocyte antigen complex is a cluster of extensively studied genes located on short arm of chromosome 6.Some of the important genes in this region are HLA class I and HLA class II genes.The important function of these HLA molecule is that they bind peptide antigens and present them to T cells, thus they are responsible for antigen recognition by the T cell receptor.Important feature of Human MHC gene products. Class IClass IIGenetic lociHLA-A , B CHLA-DP, D Q D RCell distributionAll nucleated somatic cellsAntigen presenting cells macrophages, B cells etc. activated human T cells.Present peptide antigens toCD8T CellsCD4 T cells Polypeptide compositionMolecular weight 45,000 b2 ,M MW 12000a chain M.W. 33000 b chain M.W. 29000 Li chain M.W. 30000 Other question asked on HLAHLA regulating immune response - Class II antigensHLA responsible for acceptance or rejection of allografts - Class I antigensHLA determining Histocompatibility - Class I antigenHLA which include complements of complement system - Class III antigen 