Immune Response
Pathogens
- Bacteria
o Prokaryotic Cells
o Multiply outside of host cells
o Can release toxins that harm host (like botulism)
- Viruses
o Not a cell, just nucleic acid in protein coat
o Must replicate inside host cell, using host cell enzymes
o Directly kills cells
- Parasites
o Eukaryotic cells
o Replicate outside
o Competes for nutrients and makes toxins
Innate vs acquired immunity
- innate responses are nonspecific
o protect against pathogens without specifically recognizing
- acquired responses are extremely specific
o certain cells are only activated to fight certain invaders
o recognize certain molecules or parts of molecules (antigens)
Innate Immune Responses
Barriers to entry
- skin
o physical barrier
- mucus membranes
o mucus
o things get stuck in it
o has enzyme lysozyme – breaks down bacterial cell walls
Internal defenses
- recognize molecules characteristic of particular types of pathogens
o many bacteria make lipopolysaccharide in cell wall
o many viral infections result in dsRNA being produced
- phagocytic white blood cells activated by these
o leukocytes
§ neutrophils
§ macrophages
§ others too
· eosinophils
· basophils
- nonspecific responses to infection
o inflammation
§ caused by chemicals released from cells like mast cells
§ blood vessels dilate
· more immune cells in blood get there
· vessels leaky, so cells can exit blood vessels easier
o antimicrobial peptides and proteins
§ interferons
· released by virally infected cells
· causes other cells to be less likely to be infected
§ complement proteins
· recognizes bacteria and creates pore in cell wall
Acquired Immune Response
Specifically recognizes a particular pathogen
Lymphocytes
- these are the cells of the acquired immune response
- come in two types (all are born in bone marrow)
o those that mature in the bone marrow are B cells (originally named for bursa, an organ in which they mature in chickens)
o those that go to thymus to mature are T cells
- these cells then move to secondary lymphatic organs (Fig. 53.5)
- after that they circulate around body in blood stream, back and forth to tissues and then returning to a secondary lymphatic organ
o they leave organ through lymphatic system
o may spend time in lymph nodes
o enter blood
o go around in blood
o return to secondary lymphatic organ
o repeat
- stay inactive until stimulated by encountering a specific molecule (viral, bacterial, recognized as foreign - antigen)
Overview of immune response (Fig. 53.6)
- three stages
o antigen encounter and recognition
o lymphocyte activation and cell division to produce effector cells and memory cells
o attack on pathogen
- antigen encounter and recognition
o cells express a cell surface receptor, designed to bind a particular antigen (recognition)
§ each can recognize just a single antigen
- lymphocyte activation
o binding of antigen to receptor activates lymphocyte
o it divides
o produces
§ effectors – these cells fight the pathogen
§ a small number of memory cells – these are long lived and help the next immune response to antigen be faster
- attack
o B cells make and release antibodies into blood, these result in pathogen destruction/inactivation in blood
§ Antibodies also called immunoglobulins
o T cells directly kill pathogen, such as virus infected cell or a bacterial cell
B cell receptor and antibody production
- B cell receptor (Fig. 53.7)
o Immunoglobulin protein
o 2 heavy chains
o 2 light chains
o Transmembrane domain in heavy chain
o Antigen binding site at the tips (variable region) (other is constant region)
§ When activated, differential splicing produces receptor that is soluble, having exactly same variable region