Figure 1.

(A) The human leukocyte antigen (HLA) genes are located in chromosome 6. The Class I genes (A, B, and C) are recognized by cytotoxic CD8 T-cells whereas the Class II genes that are relevant for narcolepsy are recognized by helper CD4 T-cells. HLA Class II molecules such as HLA DQ are α/β heterodimers encoded by two genes, DQA1 and DQB1. (B) Antigen presenting cells take up the antigen. The antigen is then presented to T cells (CD4 T cells in the case of HLA class II genes) by the HLA molecules. If the antigen-HLA combination is recognized by T cells, an immune reaction takes place and the cells containing the antigen may be destroyed.