HLA class I and II

HLA (Human Leukocyte Antigen) class I and II are molecules found on the surface of cells that help the immune system recognize and distinguish between the body's own cells and foreign invaders like viruses or bacteria. HLA class I molecules are present on nearly all cells and present tiny pieces of proteins from inside the cell to immune cells, alerting the immune system if a cell is infected or abnormal. HLA class II molecules are mainly on immune cells that help activate other immune cells by displaying foreign protein fragments. Together, they play a crucial role in immune surveillance and response.