T helper cells

T helper cells, also known as CD4+ T cells, are a type of T cell that play a crucial role in the immune system, particularly in the adaptive immune response. These cells help activate and direct other immune cells, coordinating the body's response to various pathogens and infections. T helper cells are essential for the immune system's ability to combat disease and infection effectively.

Classification

T helper cells are primarily classified into several types based on their function and the cytokines they produce. The main types include:

• Th1 cells - These cells are involved in the response to intracellular bacteria and viruses. They help activate macrophages and are crucial for cell-mediated immunity.
• Th2 cells - Th2 cells assist in the defense against extracellular parasites like helminths and play a role in allergic responses. They are involved in the stimulation of B cells to produce antibodies.
• Th17 cells - These cells are involved in the response to extracellular bacteria and fungi. They are known for their role in inflammatory processes and autoimmune diseases.
• Tfh cells (Follicular helper T cells) - Tfh cells are essential for the formation of germinal centers and help B cells produce high-affinity antibodies.
• Regulatory T cells (Treg cells) - These cells help maintain immune tolerance and prevent autoimmune diseases by suppressing other effector T cells.

Function

T helper cells are activated by antigens presented to them by antigen-presenting cells (APCs) such as dendritic cells. Once activated, they proliferate and differentiate into one of the subtypes mentioned above, depending on the cytokine environment and the nature of the antigen.

The primary function of T helper cells is to secrete cytokines, which are signaling molecules that mediate and regulate immunity, inflammation, and hematopoiesis. The type of cytokines produced by T helper cells dictates the type of immune response that will be generated.

Clinical Significance

T helper cells are crucial in the context of many diseases. They are famously targeted by HIV, which leads to their depletion, especially in untreated HIV/AIDS, resulting in immunodeficiency.

Moreover, an imbalance in T helper cell responses can lead to autoimmune diseases, where the immune system attacks the body's own tissues. Examples include multiple sclerosis and rheumatoid arthritis, where Th1 and Th17 cells play a detrimental role.

Research

Research on T helper cells continues to be a significant field in immunology. Scientists are exploring ways to modulate T helper cell responses to improve vaccine efficacy and treat autoimmune diseases, allergies, and other immune-related conditions.

See Also

• Immune system
• Cytokine
• Autoimmune disease
• Vaccine