Class II human antigens, also known as human leukocyte antigens (HLA), are cell surface proteins found in humans that play a crucial role in the immune system. They are a part of the major histocompatibility complex (MHC) system, which is responsible for distinguishing self from non-self molecules, and facilitating the recognition and response to foreign substances.
Class II human antigens are encoded by genes located on chromosome 6 in humans. These genes are highly polymorphic, meaning they exhibit a wide range of genetic variations among individuals. This polymorphism enables the immune system to recognize and respond to a diverse array of pathogens.
The Class II human antigens are primarily expressed on certain immune cells, including antigen-presenting cells such as macrophages, dendritic cells, and B cells. Their primary function is to present antigens, derived from internalized pathogens or other foreign agents, to helper T lymphocytes. This presentation triggers the activation and proliferation of T cells, leading to a coordinated immune response against the specific pathogen.
The presence or absence of specific Class II human antigens on immune cells is a crucial determinant in transplant compatibility, as it dictates whether an immune response will be mounted against transplanted tissues. Matching HLA types between the donor and recipient increases the likelihood of successful transplantation.
In addition, Class II human antigens are involved in various autoimmune diseases, where the immune system mistakenly attacks normal tissues. These antigens are also important in the development and progression of certain infectious diseases and cancers.
Overall, Class II human antigens are essential components of the immune system, enabling the body to recognize, respond to, and regulate immune responses against foreign substances.
