chapter 25

neutrophils

actively mobile granulocytes (neutrophilic indicates active infection response)

monocytes

precursors of macrophages/DCs

• large cells found in tissues such as lymph nodes and spleen, also in circulation

macrophages

large, non circulating, phagocytic cell found in most tissue (up to 10-15% of tissue), essential for innate and adaptive response (APC)

dendritic cells

function in phagocytosis and antigen presentation; immature found throughout tissue, activated migrate to lymph nodes to present

• when they ingest antigen, they move to the lymph node to present antigen to T cells

phagocytes recognize a pathogen using…

pattern recognition receptors (PRRs) also called TLRs

• membrane-bound phagocyte proteins that recognize pathogen-associated molecular patterns (PAMPs)

what does the activation of certain genes in phagocytes do?

enhances phagocytic and pathogen-killing abilities

• use toxic oxygen to kill ingested bacterial cells by oxidizing key cellular constituents

• occurs within phagolysosome (not damaged by the toxic oxygen products)

name some pathogens which have developed mechanisms for neutralizing toxic phagocytic products

S. aureus (carotenoids) and M. tuberculosis (cell wall glycolipids absorb hydroxyl radicals and superoxide ions — the most lethal oxygen species)

some intracellular pathogens produce…

leukocidins that kill the phagocyte (S. aureus and S progenes produce M protein to alter surface and prevent phagocytosis)

some bacteria produce…

a capsule resistant to phagocytosis like S. pneumoniae

what are 3 adaptive response properties?

1. T lymphocytes recognize the peptide antigens through TCRs

2. cell-mediated immunity = pathogen-infected host cells are killed after they are recognized via pathogen antigens found on their surface (via MHC1) (TC) or pieces that have been taken in by phagocytosis and displayed (via MHC2) activate macrophages to proliferate, find, kill (TH1)

3. antibody-mediated immunity = effective against extracellular pathogens such as bacteria and soluble pathogen products

define memory in the context of the immune response

subsequent exposures to the same antigen result in rapid production of large quantities of antigen-reactive T cells or antibodies » clonal expansion = multiplication of antigen-reactive cells, then the immune response is faster and stronger due to large number of responding cells

what is tolerance?

acquired inability to make an adaptive immune response to one’s own antigens; self-reactive cells are destroyed during development of the immune response (clonal deletion)

• discrimination between foreign and host antigens

what are intrinsic properties of immunogens?

1. size (like happens are low molecular weight so they are antigens but not immunogens)

2. complexity

3. form (solubility)

what are extrinsic properties of immunogens?

1. dose

2. route

3. foreignness

does the antibody or TCR interact with the whole antigenic macromolecule?

NO, only with a distinct portion of the molecule called an epitope

T-cytotoxic (Tc) cells

T cells that directly kill cells that display surface foreign antigens

• contact between these and target cell is required for cell death

• first MHC/TCR binding, then CD8/MHC bind, strengthen interaction

• on contact, granules in T cell migrate to contact site

• degranulation occurs and causes pores (perforin) in target cell membrane

• also contain granzymes that cause apoptosis

• cells lacking antigen are not killed