Other Cells of Immune System Dr Shoaib Raza

Dendritic Cells Numerous fine cytoplasmic processes Dendritic cells (Interdigitating) Potent APC Present under epithelial cells Immature dendritic cells are Langerhans cells Express receptors for capturing microbes Germinal centers of lymphoid organs Follicular dendritic cells Have Fc receptors for IgG

Macrophages Phagocytosis APCs and T-Cell activation Receptors for Fc portion of IgG and C3b, induce humoral immunity

Natural Killer Cells Large granular lymphocytes 10-15% of circulating lymphocytes Part of innate immunity Kill a variety of tumor cells and virally infected cells without prior sensitization

Major Histocompatibility Complex Responsible for tissue compatibility Function of MHC is to display peptide fragments of proteins for recognition by antigen-specific T-Cells Genes present on chromosome 6 HLA or MHC On the basis of structure, cellular distribution, and function Class I MHC Class II MHC

Class I MHC Expressed on all nucleated cells and platelets HLA-A, HLA-B, HLA-C Heterodimer consists of polymorphic α (heavy) chain, and a smaller nonpolymorphic peptide, β2 microglobulin Class I molecules display peptides derived from proteins e.g. viral antigen Recognized by CD8+ T-Cells (cytotoxic T lymphocytes)

Class II MHC Expressed in HLA-D HLA-DP, HLA-DQ, HLA-DR Each class II molecule is a heterodimer consists of α and β chains Class II MHC present antigens that are internalized into vesicles, and are typically derived from extracellular microbes and soluble proteins Present antigens to CD4+ T lymphocytes (helper cells)

HLA and disease association Ankylosing spondylitis HLA-B27 Rheumatoid arthritis DR4 Chronic active hepatitis DR3 Primary Sjogren syndrome DR3 Type 1 Diabetes mellitus DR3/DR4

Cell Mediated Immunity Upon antigenic stimulation CD4+ T cells are activated TH1 IFN-γ IL-12 TH2 IL-4, IL-5 IL-4 IL-13 TH17 IL-17, IL-22 TGF-β, IL-6, IL-1, IL-23