2A - T Lymphocytes, MHC, and Tolerance

Question 1

T-lymphocytes ( type of immunity, origin and maturation, residence

Answer 1

‣ Cell mediated immunity (cells do the work)
‣ Originated in the bone marrow and mature and differentiate in the thymus
‣ Reside in the peripheral lymph nodes
◦ Are specific and have memory

Question 2

types of T-lymphocytes

Answer 2

Cytotxoic (CD8+) and T Helper (CD4+)

Question 3

Cytotoxic T cells role and markers

Answer 3

( CD8+)

‣ Kill infected or damaged host cells

Question 4

T Helper cells role and markers

Answer 4

(CD4+)
‣ Th1 cells stimulate cytotoxic T lymphocytes and macrophages
‣ Th2 cells stimulate B lymphocytes to make more antibodies

Question 5

Retroviruses that infect CD4+ T helper cells

Answer 5

• HIV and FIV are both Retroviruses that infect CD4+ T helper cells

Question 6

HIV and FIV infection causes

Answer 6

‣ Gain entry to the cell via the CD4 receptor on the cell surface
‣ Causes an immunodeficiency very specific to Th inactivity
◦ Opportunistic infections
◦ Certain types of cancers

Question 7

Treg

Answer 7

• Regulatory T lymphocytes
◦ Produce immunosuppressive and anti-inflammatory cytokines
◦ Down regulate antibody production

Question 8

MHC

Answer 8

• Major Histocompatibility Complex
◦ a complex of genes that code for specialized molecules on the cell surface involved in intracellular recognition and distinguishing of self from non-self

Question 9

MHC function

Answer 9

◦ Most T cells only recognize antigen when it is bound to MHC
◦ Helps T lymphocytes recognize “self” vs “non-self”

Question 10

Antigen processing and presentation

Answer 10

• Antigen is processed in phagocytic cells like macrophages, the antigen is degraded into peptide fragments which are complexed with the MHC molecule
• Antigen is presented - the MHC-Ag complex is transported to the cell membrane surface and displayed

Question 11

Antigen

Answer 11

any molecule that stimulates immune system (either innate or adaptive)

Question 12

MHC1 function

Answer 12

• Intracellular antigens are processed inside the cell and are presented with MHC1 molecules
◦ MHC1 molecules are present on all nucleated cells
◦ MHC 1 stimulates Cytotoxic T cells (CD8+) to kill the infected or neoplastic cells

Question 13

MHC2 importance and function

Answer 13

only present on antigen presenting cells such as macrophages and dendritic cells
◦ Class 2 MHC stimulates T -Helper cells
◦ Remember T-helper cells stimulate B-lymphocytes to make antibody
‣ Extracellular antigens are degraded inside a phagocytic cell, bind with MHC 2 molecules and are then presented on the cell surface
• Floating in the body, taken in by macrophage

Question 14

T and B lymphocyte differentiation

Answer 14

T-cells undergo differentiation, selection and maturation in the thymus
◦ B cells in birds differentiate in the Bursa of Fabricius or in mammals undergo differentiation in both the bone marrow and in the lymph nodes

Question 15

Auto-immune disease and other immune response

Answer 15

an inappropriate immune response to self antigens
normal - When exposed to an antigen and the immune system may be responsive and develop a state of immune response or it can be non-responsive and develop a state of tolerance

Question 16

Centeral tolerance

Answer 16

Clonal Deletion of self-reactive T lymphocytes occurs when the T cells are developing in the thymus

Question 17

Peripheral tolerance

Answer 17

◦ When the T cells are mature and out in the lymph nodes

‣ MHC is integral to development of tolerance (name tag)

Question 18

Sequestered antigens and why they are hidden from the immune system

Answer 18

◦ Examples of sequestered antigens are myelin protein, lens protein and sperm protein
◦ Release of these proteins due to infection or trauma may lead to an immunological response by lymphocytes that react against these proteins → autoimmune response → failure of self tolerance
‣ Ex uveitis, spermatic granuloma

Question 19

NK cells size and importance

Answer 19

mononuclear but have granules smaller than monocytes but are larger then lymphocytes
◦ NK cells are important in the innate immune response and have a non-specific response
◦ They are important in early response to tumor cells and viral infections, and other intracellular pathogens
◦ Does not require specific antigen

Question 20

NK cells difference from other T lymphocytes

Answer 20

• Unlike Cytotoxic T lymphocytes, NK cells attack cells that do not express MHC
◦ Virus infected cells and neoplastic cells may not express MHC and this makes them susceptible to NK attack