The immune system is a complex network of cells and proteins that protect the body from foreign invaders and maintain health. A key part of this communication system involves signaling molecules called cytokines. These proteins act as messengers, allowing immune cells to communicate and coordinate a defense response. Th2 cytokines represent a specific group of these signaling molecules, playing a part in various immune responses.
What Are Th2 Cytokines
Th2 cytokines are proteins primarily produced by T helper 2 (Th2) cells. T helper cells guide other immune responses, directing other immune cells. Beyond Th2 cells, other cells such as mast cells, basophils, and eosinophils can also produce these cytokines.
Key Th2 cytokines include Interleukin-4 (IL-4), Interleukin-5 (IL-5), and Interleukin-13 (IL-13). IL-4 stimulates B cell proliferation and differentiation, and aids Th2 cell development. IL-5 stimulates production and activation of eosinophils, a type of white blood cell. IL-13 has functions similar to IL-4, influencing B cell activity and contributing to processes like mucus production. These cytokines collectively direct specific immune actions, such as promoting antibody production and recruiting certain immune cells.
Their Role in Protection
Th2 cytokines play a beneficial role in the immune system, particularly in defending against specific threats. A primary function involves protecting from parasitic infections, such as worms. These cytokines help coordinate responses that lead to parasite expulsion.
Beyond combating parasites, Th2 cytokines also contribute to tissue repair after injury or infection. For instance, IL-4 and IL-13 activate macrophages, important for wound healing and extracellular matrix. This repair mechanism helps maintain tissue integrity. These functions highlight the roles of Th2 cytokines in maintaining immune defense and facilitating recovery.
When Th2 Responses Go Awry
While protective, Th2 cytokine responses can become overactive or dysregulated, leading to various health issues. An exaggerated Th2 response is significantly involved in common allergic diseases. These conditions include asthma, allergic rhinitis (hay fever), and atopic dermatitis (eczema).
In allergic asthma, for example, Th2 cytokines like IL-4, IL-5, and IL-13 promote inflammation in the airways. IL-5 specifically contributes to the increase and survival of eosinophils, which are often found in high numbers in the airways of asthmatic individuals. IL-4 and IL-13 can induce increased mucus production and airway hyperresponsiveness, which are characteristic symptoms of asthma.
Similarly, in allergic rhinitis and atopic dermatitis, Th2 cytokines drive inflammatory processes. IL-4, IL-5, and IL-13 contribute to symptoms such as itching, redness, and skin thickening in atopic dermatitis by activating immune cells like eosinophils and mast cells. An imbalance in Th2 responses, while normally protective, can thus contribute to chronic inflammatory states seen in these allergic conditions.