The Human Leukocyte Antigen (HLA) is the one type of antigen present in the Major Histocompatibility Complex (MHC). It plays a crucial role in the MHC’s function. 

There are various types of HLA present in MHC Class I and MHC Class II. 

• The three types of HLAs present in MHC Class I are HLA-A, HLA-B and HLA-C. 
• The three types of HLAs present in MHC Class II are HLA-DR, HLA-DQ, and HLA-DP.

HLA is responsible for identifying foreign substances within the body. It first detects whether a substance is foreign. If the substance originates from the body, the appropriate HLA signals MHC Class I. If the substance is a foreign antigen that has not originated from the body, the HLA signals MHC Class II, triggering an immune response.