T-Cell Maturation: Events in the Thymus

Functions of T Cell Subtypes

• Th-1 cells primarily promote cell-mediated immunity during infections, facilitating the response to intracellular pathogens.
• Th-2 cells are responsible for stimulating humoral immunity and are particularly effective against extracellular parasites; they mediate antibody production.
• Th-17 cells play a crucial role in defending against fungal and bacterial infections, promoting inflammation and tissue repair.

T Cell Development and Selection

• Negative selection in the thymus eliminates T cells that strongly recognize self-antigens, helping to prevent autoimmune diseases.
• High-affinity antigen receptors for self-antigens lead to T cell deletion during negative selection to maintain self-tolerance.

Cytokines in T Cell Activation

• Interleukin-2 (IL-2) is essential for T cell maturation and expansion, promoting the growth and differentiation of T cells following activation.
• IL-12 contributes to the differentiation of naïve T cells into Th-1 cells and enhances the activity of cytotoxic T lymphocytes (CTLs) and natural killer (NK) cells.

Chemokines and the Inflammatory Response

• Chemokines serve as signaling proteins that direct the migration of immune cells to sites of infection or injury, playing a critical role in inflammatory responses.
• Activation of chemokines results in gene switching in B cells, leading to the production of different classes of antibodies (isotypes).

Clinical Significance and Diagnosis

• A CD4 count below 120 cells/ml indicates severe immunosuppression, increasing susceptibility to opportunistic infections.
• A viral load exceeding 110,000 copies/ml signifies high levels of virus in the bloodstream, suggesting active viral replication and potential disease progression.

Treatment Implications

• Recommended treatments for patients depend on the examination results, which may include antiviral therapies and supportive care based on immune status and viral load.