===== Th1 =====

=== 1. Neuroanatomy: Thoracic Spinal Segment 1 (T1) ===
**Th1** refers to the **first thoracic spinal segment**.

==== Location ====
  * Situated between cervical segment C8 and thoracic segment T2
  * Corresponds approximately to the **first thoracic vertebra (T1)**

==== Function ====
  * Origin of **spinal nerves T1**, which contribute to:
    * **Brachial plexus** (particularly the inferior trunk)
    * **Sympathetic preganglionic neurons** in the **intermediolateral cell column** (IML)
  * Part of the **thoracolumbar outflow** of the **sympathetic nervous system**

==== Clinical Relevance ====
  * Lesions at Th1 may cause:
    * **Horner syndrome** (ptosis, miosis, anhidrosis) due to disruption of sympathetic fibers
    * Motor or sensory deficits in the medial arm/forearm

=== 2. Immunology: T Helper 1 Cells (Th1) ===
**Th1** cells are a subtype of **CD4+ T helper lymphocytes** that orchestrate the **cell-mediated immune response**.

==== Function ====
  * Activate **macrophages** and **cytotoxic T cells**
  * Promote defense against **intracellular pathogens** (e.g., viruses, some bacteria)

==== Cytokine Profile ====
  * Secrete **Interferon-gamma (IFN-γ)**, **IL-2**, **TNF-α**
  * Stimulated by **IL-12** (from dendritic cells/macrophages)

==== Clinical Relevance ====
  * Th1 dominance is associated with:
    * **Autoimmune diseases** (e.g., type 1 diabetes, multiple sclerosis)
    * Resistance to **tuberculosis**
  * Imbalance between **Th1/Th2** responses affects immunity and hypersensitivity patterns

==== Related Entries ====
  * [[neuroanatomy:thoracic_spinal_cord]]
  * [[autonomic_nervous_system:thoracolumbar_outflow]]
  * [[immunology:t_helper_cells]]