Chapter Intro

Innate Immune System

• Microbial recognition: PAMPs on microbes are recognized by TLRs on immune cells
• Non-specific part of immune system
• Cellular factors:
• Macrophages (phagocyte and antigen presenting cell)
• Dendritic cells (phagocyte and antigen presenting cell) --> link innate and adaptive immunity
• Neutrophil (phagocyte; combines with bacteria and NET to form pus)
• Mast cells, basophil (granulocyte, secrete histamine)
• Eosinophil (kill parasites and allergic reactions)
• Natural killer cell (kill virus-infected cells)

• Humoral factors:
• Cytokines
• Complement (cascade)
• Tags or punch holes on invading pathogens
• Can be activated on antibodies
• Classical pathway activated on IgM and IgG antibodies
• Classical signs of inflammation: rubor, dolor, calor and tumor

Adaptive Immune System

• More specialized --> creates memory
• Cellular factors:
• T cells: CD4+ (bind to MHC II) or CD8+ (bind to MHC I)
• CD4+ = helper T cells (TH1, TH2, TH17 or Treg)
• CD8+ = cytotoxic, kills virus-infected cells
• Produced in bone marrow and mature in the thymus
• Undergo positive and negative selection
• Interactions with other cells usually require co-stimulation signal
• APC <-> T cells = B7 and CD28 are co-stimulation signal
• B cell <-> T cells = CD40L and CD40 are co-stimulation signal
• CTLA4 or PDL1 are molecules on tumors (or other cells) that inactivate T cells

• B cells: produce antibodies
• Immunoglobulins are B cell receptor: IgM or IgD
• Produced and mature in bone marrow (express rag 1/2)
• Can undergo VDJ recombination to produce antibody diversity
• Switching between antibody classes requires help from Th2 helper T cells

• Major histocompatibility complex (MHC)
• Identity tags and how cells present antigens to T cells
• MHC I = all cells have
• MHC II = only APCs have
• APCs are:
• B cells
• Dendritic Cells
• Macrophages

• Humoral factors:
• Antibodies:
• Serve to enhance phagocytosis = opsonization
• Antibody class = look at heavy chain
• Fab = binds antigen, Fc = binds phagocyte
• IgM: first produced, fixes complement, in circulation as a pentamer/monomer as B cell receptor
• IgG: later produced, fixes complement, Fc portion binds to phagocytes, neutralizes toxins/opsonization
• IgA: secretory antibody, secreted into mucus, tears, saliva, in circulation as dimer
• IgE: binds to mast cells/basophils for allergy or parasites
• IgD: can be B cell receptor