T2 cells are a specialized type of white blood cell, belonging to the broader family of T helper cells within the immune system. They are a component of the adaptive immune system, capable of recognizing and reacting to specific signals, playing a part in the body’s defense mechanisms.
The Primary Role of T2 Cells
T2 cells play a role in the body’s defense against certain types of invaders, particularly large extracellular parasites like helminths. The immune response orchestrated by T2 cells helps to expel these organisms from the body.
Beyond combating parasites, T2 cells also contribute to tissue repair and wound healing. When tissues are damaged, T2 cells and the molecules they produce can help in the resolution of inflammation and the reconstruction of injured tissue. This involves activating M2 macrophages, which aid in healing.
How T2 Cells Communicate
T2 cells exert their effects by releasing specific signaling proteins called cytokines, which act as messengers to other immune cells and body tissues. Three prominent cytokines produced by T2 cells are Interleukin-4 (IL-4), Interleukin-5 (IL-5), and Interleukin-13 (IL-13).
Interleukin-4 (IL-4) instructs B cells to produce Immunoglobulin E (IgE) antibodies, which are commonly associated with allergic reactions. IL-4 also influences mucus secretion, airway remodeling, and the recruitment of eosinophils.
Interleukin-5 (IL-5) signals eosinophils, promoting their growth, survival, and activation. Eosinophils are recruited to sites of inflammation where they release substances that contribute to immune responses.
Interleukin-13 (IL-13) increases mucus production in the airways, impacting lung function. It also contributes to changes in the skin barrier, potentially impairing its protective function, and affects smooth muscle contraction in tissues like the airways. Like IL-4, IL-13 also promotes IgE production and eosinophil recruitment.
T2 Cells and Allergic Diseases
An overactive T2 immune response contributes to several common allergic diseases. This occurs when the body reacts strongly to normally harmless substances, such as pollen or dust mites. The cytokines released by T2 cells directly generate the symptoms experienced in these conditions.
In asthma, particularly T2-high asthma, elevated T2 cell activity leads to eosinophilic inflammation within the airways. IL-5 recruits and activates eosinophils, while IL-13 increases mucus production and makes airways more responsive to triggers, leading to symptoms like wheezing, coughing, and shortness of breath. The chronic inflammation can also result in structural changes in the airways over time.
Atopic dermatitis, also known as eczema, is a chronic inflammatory skin condition characterized by dry, itchy, and inflamed skin. IL-4 and IL-13 contribute to the disruption of the skin barrier, making it more permeable to allergens and irritants. This breakdown in barrier function, combined with increased IgE production, leads to characteristic itching and inflammation.
Allergic rhinitis, or hay fever, involves inflammation of the nasal lining, causing symptoms like sneezing, a runny nose, and nasal congestion. IL-4 drives IgE antibody production, which binds to mast cells in the nasal passages. When allergens are encountered, these mast cells release histamine and other mediators, triggering immediate allergic symptoms. IL-13 further contributes to increased mucus secretion in the nasal mucosa.
Targeting T2 Cells in Medicine
Modern medical strategies for managing T2-driven allergic diseases involve targeting specific components of the T2 immune pathway. These advanced treatments, often called “biologics,” are monoclonal antibodies designed to interfere with precise molecular signals. Unlike general immune suppressants, biologics offer a more focused treatment approach.
These drugs block the activity of specific cytokines or their receptors, interrupting the chain of events that leads to allergic inflammation. For instance, some medications neutralize IL-5, preventing it from activating eosinophils. This reduces inflammatory cells at sites like the lungs.
Other biologics, such as dupilumab, block the shared receptor subunit for both IL-4 and IL-13. By inhibiting the signaling pathways of these two cytokines, dupilumab reduces IgE production, eosinophil recruitment, and other inflammatory processes that contribute to conditions like asthma, atopic dermatitis, and allergic rhinitis. This targeted approach aims to reduce symptoms and improve disease control by dampening the overactive T2 response.