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How do major histocompatibility complex molecules help T cells detect infection?

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Immune stimulation by activated helper T cells — immune system Stimulation of immune response by activated helper T cells. Activated by complex interaction with molecules on the surface of a macrophage or some other antigen-presenting cell, a helper T cell proliferates into two general subtypes, T_H1 and T_H2. These in turn stimulate the complex pathways of the cell-mediated immune response and the humoral immune response, respectively.

Major histocompatibility complex (MHC) molecules are essential for the immune system because they allow T cells to detect and respond to infections that are otherwise hidden from circulating antibodies.12

When a cell is infected by a pathogen or ingests a microorganism, it partially digests the invader and displays small peptide fragments on its surface. These fragments are bound to MHC molecules, which act as a platform for presentation to T cells.12

The detection process relies on specific interactions:
* Class I MHC molecules: Found on almost all nucleated cells, these present antigens to cytotoxic T cells, which can then destroy the infected or cancerous cell.12
* Class II MHC molecules: Restricted to specific immune cells like macrophages and B cells, these present antigens to helper T cells, which help coordinate the broader immune response.132

T cells use their T-cell receptors to recognize the specific foreign peptide-MHC complex, while coreceptors like CD4 or CD8 provide additional binding strength to ensure an accurate immune response.24