Immunology (Feldman and Baum) Flashcards
Extracellular pathogen response
MHC-II
CD4 Th2 cells
Antibodies
Intracellular bacteria or fungus response
MHC-II
CD4 Th1 cells
Macrophages become poisonous
Intracellular virus response
MHC-I
CD8 cytotoxic lymphocytes
Kill viral infected cells
What causes expression of B7 on APC?
TLR on APC tickled by PAMP on foreign invader –> cytokines released –> B7 expressed on APC surface
Thus, B7 (second signal) ONLY expressed on cells that have seen PAMP
Fluid circulation from blood to lymph
1) Pressure drives fluid out of capillaries and into tissue
2) Blunt end of lymphatics drain fluid (containing APCs) in tissues and take it into lymphatic system
3) Afferent lymphatic
4) Regional lymph node
5) Thoracic duct
6) Superior vena cava
7) Arterial blood system
How do naive lymphocytes and APCs and antigens get into the lymph node?
Naive B and T cells: high endothelial venule (HEV)
APCs and antigens: afferent lymphatics
Spleen
Red pulp: RBCs, WBCs (neutrophils)
White pulp: B and T cells
Screens blood for antigen; macrophages ingest old RBCs and platelets
Hyper IgM Syndrome
T cell defect (lack of CD40L) so B cells cannot do somatic hypermutation and class switching, so continue to secrete IgM.
No germinal centers
Susceptibility to bacterial infections because can’t opsonize bacteria
What happens immediately when foreign invader breaches epithelial barrier?
1) Phagocytes (neutrophils, macrophages) can phagocytose, secrete toxic enzymes, destroy pathogens
2) DCs (Langerhans cells) can also phagocytose, go to lymphoid tissue, present on MHC to connect to adaptive immunity
3) Phagocytes secrete cytokines to increase local inflammatory response
MHC binding
Degenerate (less specific, can bind multiple different peptides)
Low affinity
Very slow off rate (good because give MHC-peptide time to find and interact with T cell)
Polysaccharide encapsulated bacteria defense (adults vs. children)
Adults have T-cell independent antibody response to polysaccharide encapsulated bacteria (bacterial cell wall and capsular polysaccharides with highly repetitive structures are TI-2 antigens)
Note: we cannot use mannose-lectin or alternative complement pathway for encapsulated bacteria
Children do not have this response. Can use conjugate vaccine so they don’t get lots of infections from encapsulated bacteria.
Conjugate vaccine
1) Repetitive polysaccharide coupled to protein from same encapsulated bacteria.
2) Complex binds BCR through polysaccharide but presents protein on MHC.
3) T cell recognizes MHC-peptide on B cell and activates B cell to make antibodies to whatever B cell originally bound (the polysaccharide)
Thus, children/people vaccinated with conjugate vaccine can make a T-cell dependent antibody response to encapsulated bacteria even though we normally cannot
Type I Immune Response
Allergy and Anaphylaxis
IgE mediated mast cell degranulation
Presence of eosinophils is indicative (also have mast cells and plasma cells)
Type II Immune Response
Antibody mediated (on cell surface)
Complement destroys cells coated with antibodies
Type III Immune Response
Antibody-Antigen Complex mediated
Immune complexes formed usually with IgM or IgG and SOLUBLE antigens
Deposition of immune complexes on blood vessel walls or in tissues –> inflammation, complement activation
