Cells of the Immune System

Overview

Introduction

• The immune system involves cells from two major lineages including 
  • lymphoid cells derived from a lymphoid progenitor such as
    • natural killer (NK) cells
    • T-lymphocytes
    • B-lymphocytes
  • myeloid cells derived from a myeloid progenitor such as
    • mast cells
    • basophils
    • neutrophils
    • eosinophils
    • monocytes
    • macrophages
• These cells carry out many of the major roles of the immune system including
  • phagocytosis of invading microbes
  • secretion of the protein components of humoral immunity such as
    • antibodies
  • production of toxic substances such as
    • reactive oxygen species
• direct cytotoxic signals through receptor based interactions

Lymphoid Cells

• Lymphoid cells can broadly be divided into four classes including
  • NK cells that kill cells without major histocompatability complexes (MHC)
  • T-cells that can be further subdivided into
    • killer T-cells that are directly cytotoxic
    • helper T-cells that enable other immune functions
    • regulatory T-cells that maintain immune tolerance
• B-cells that mediate humoral immunity

• Helper T-cells (CD4+ cells) can be further subdivided into classes based on function

Myeloid cells

• Myeloid cells perform a large variety of innate immune functions including
  • phagocytosis of invading antigens
  • secretion of cytokines and immunoactive proteins
  • clearance of cellular debris
  • presentation of antigens to adaptive immune system
  • alteration of vascular physiology
• Different innate immune cells are specialized for different functions