# Lymphocytes
## Introduction
- T-Lymphocytes (Thymus): cellular
- B Lymphocytes (Bone Marrow): humoral
- NK (Natural Killer)
- Most undergo further antigen-mediated differention in lymphoid organs, but not a small subset of CD4+T
- CD4+T and CD8+T majorty of T-Lymphocytes

## CD4T+
- Effector subtypes
- Activate Innate Immune, B, Cyto-T, and other cells
- Suppress immune reaction
- Subtypes: Th1, Th2, Th-17, Tfh, iTreg, Tr1, Th9

## Lymphopoiesis
- Thymocytes from hematopoietic stem cell (marrow) come to thymus
- Thymus: primary lymphoid organ provides microenvironment of stromal cells, cytokines and chemokines to generate T-cells from thymocytes
- Gene rearrangement and thymocyte selection
- Affinity model (to peptide complex on Antigen-presenting cells APC):
  - low affinity thymocytes die
  - high affinity are destroyed
  - intermediate affinity are differentiated into CD4/8+
- CD4+: nTreg, NKT (also CD4-CD8-), mature-naive
- CD8+: MHC1b, MR1 mucosa-associated

## Activation and Differentiation
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