antigen processing

• dendritic cell

  present to naive T cell, results in clonal expansion and differentiation onto effector T cells (CD4 T and CD8 T)
• macrophages

  present to effector T cell, causes effector T cells to secrete IFN-y to activate macrophages (cell mediated immunity)
• b cells

  present to CD4 T cells, that help the B cell generate high affinity antibodies and memory
• CD4 T cells

  differentiate into helper T cells and interact with MHC 2
• CD8 T cells

  differentiate into CTL and interact with MHC 1
• B lymphocytes

  bind unprocessed antigen (antigen can be soluble or cell bound) and differentiate into plasma cells
• CD4 t cells require processed antigen (usually exogenous), and recognise via MHC class 2
• CD8 t cells require processed antigen (usually endogenous), and recognise via MHC class 1
• endogenous processing

  synthesised within the cell, eliminated by CD8 T cells
• exogenous antigen processing

  eliminated by antibodies
• cross presentation

  APCs present extracellular antigens with MHC class 1 to CD8 T cells. this is important for immunity against tumours and against viruses
• endogenous antigen processing

  intracellular proteins are marked for degradation. peptides enter the ER and are associated with MHC class 1. MHC class 1 + peptide are transported to cell surface. complex interacts with TCR
• exogenous antigen processing

  extracellular proteins endocytose into the cell and are degraded by proteases, endosomes fuse with MHC class 2. complex interacts with TCR or an CD4 T cell
• cross presentation

  APCs take up, process, and present exogenous antigens via MHC class 1 to CD8 T cells. this is important for immunity against viruses and tumours that don't infected APCs
• co stimulation

  signal 1: TCR binding to MHC + peptide. signal 2: co-stimulation. after co-stimulation, cytokines can be produced
• cells express IFN-y and IL-12 to generate Th1 cells
• cells express IL-4, which generates Th2 cells
• IL-17 and IL-22 generate Th17 cells
• IL-21 generates Tfh cells
• CD8T cells kill viruses and some intracellular bacteria
• Th1 cells activate macrophages and provide help to B cells for antibody production. target extracellular bacteria
• th2 cells provide help to B cells for antibody production, target helminths and parasites
• Tfh cells provide b cell help for isotope switching and antibody production
• Thymus dependant b cell responses

  isotope switching, high affinity antibodies, long lived plasma cells
• T independent B cell responses

  mainly IgM produced, short lived plasma cells
• B cell co-receptor complex

  CD19, 21, 81
• thymus dependant antibody production signals

  BCR complex and Tfh (via MHC class 2 and costimulation)
• Thymus dependent antibody production

  DC present to CD4 T cells, resulting in Tfh differentiation. antigen is recognised by BCR and processed. B cell presents antigen to Tfh via MHC class 2. Tfh provides co-stimulation and Il-21. B cells secrete antibodies
• Thymus independant b cell responses (TI-1)

  TI-1 cause proliferation of most b cells. relies on TLR on B cell surface and high concentrations of antigen
• Thymus independant b cell responses (TI-2)

  TI-2 antigens are highly repetitive structures and activate mature B cells through multiple cross linking of BCR. important for IgM responses against capsulated bacteria. cytokines can augment response. IgG can be produced
• IgM

  complement activation
• IgG

  opsonisation, phagocytosis, complement activation, neonatal immunity
• IgE

  against helminths, and mast cell degranulation
• IgA

  mucosal immunity