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Flashcards in Immunology (Feldman and Baum) Deck (19)
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Extracellular pathogen response


CD4 Th2 cells



Intracellular bacteria or fungus response


CD4 Th1 cells

Macrophages become poisonous


Intracellular virus response


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



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


Type IV Immune Response

Cell Mediated (CD8) or Delayed Type Hypersensitivity (CD4)

Delayed because need T cells to act, which takes a few days


Four mechanisms of tolerance

1) Clonal deletion

2) Clonal anergy

3) Peripheral suppression

4) Immunologic ignorance


Mechanisms to overcome immunological ignorance

1) Creation of new epitopes

2) Molecular mimicry

3) Polyclonal lymphocyte activation

4) Exposure of sequestered antigen


Risk factors for autoimmunity

1) Trauma

2) Infection

3) Genetic predisposition

4) Hormonal changes during puberty