Final answer:
The two types of human leukocyte antigen (HLA), or major histocompatibility complex (MHC) molecules, that interact with NK cells are MHC class I, which helps NK cells differentiate between healthy and infected or abnormal cells, and MHC class II, which is involved in antigen presentation for T cells but does not interact directly with NK cells.
Step-by-step explanation:
Interaction of HLA with NK Cells
The two types of human leukocyte antigen (HLA), also known as major histocompatibility complex (MHC) molecules, that interact with natural killer (NK) cells are MHC class I and MHC class II. NK cells play an essential role in the immune system by recognizing and destroying infected or abnormal cells, such as virus-infected cells or tumor cells. They identify these cells primarily through the altered expression of MHC class I molecules on the cell surface.
Healthy cells that express normal MHC I molecules interact with NK cells to prevent them from attacking. These molecules present fragments of proteins from within the cell to T cells, allowing the immune system to distinguish between self and non-self. In contrast, MHC II molecules, which are only found on specific immune cells like macrophages and dendritic cells, present pathogen antigens for T cells but do not interact directly with NK cells.
When a cell lacks MHC I molecules, NK cells see this as an indication of infection or abnormality and may target the cell for destruction. Hence, both MHC class I and MHC class II molecules have critical roles in the adaptive immune system; however, it's the MHC class I that plays a direct part in interacting with NK cells to avoid the killing of healthy cells and to identify infected or tumor cells for elimination.