Lymphocyte maturation

Question 1

what is the function of the thymus for lymphocytes

Answer 1

• thymic education or central tolerance of T-cells
• T-cells must be prevented from reacting to “self” antigen (learn how to tell what is foreign and what isnt)
• thymic education of T-cells begins during foetal life and continues for the first few months of life
• thereafter the thymus involutes (shrinks) - the lymphoid tissues become replased by adipose and connective tissue

Question 2

what is the function of the spleen for lymphocytes

Answer 2

• specialised lymph node for blood born antigens
• very well vascularised, byt ONLY have efferent lymphatics, part of the vascular blood system
• consists of red and white pulp areas:
• Red pulp filters blood for foreign pathogens and removes defective erythrocytes and platelets. also stores eryhtrocytes and platelets
• white pulp contains many cell types including macrophages and antigen presenting cells and aging erythrocytes, as well as T and B lymphocytes

Question 3

what is the function of the lymph nodes

Answer 3

• presentation of antigen to lymphocytes and mount and immune response if necessary
• lymph enters the node by afferent lymphatics and leaves via efferent lymphatics
• densely packed with T and B cell lymphocytes, antigen presenting cells and monocytes
• immune cells are monitoring lymph for foreign pathogens

Question 4

wher does the development of mature B cells occur in dogs

Answer 4

ileal peyers patches
- bone marrow has a role as well but secondary to peyers pathches

Question 5

describe how T lymphocytes that react with ‘self’ proteins are removed during development

Answer 5

• positive selection: T cells which recognise the bodys own MHC (I or II) are retained
• negative selection: T cells which respond to self peptides in the MHC are eliminated. T cells which ignore self peptides are retained

occurs mostly in the thymus

Question 6

what is MHC

Answer 6

• expressed on the cell surface
• controls how the immune system detects and responds to specific antigens
• main role is in antigen presentation where MHC molecules display peptide fragments for recognition by appropriate T cells
• 2 classes have a similar function involving delivery of short peptides to the cell surface for recognition by CD8+ and CD4+ T Cells respectively
• MHC class 1: on every nucleated cell - presents endogenous (self) peptides
• MHC class 2: on antigen presenting cells (B cells, dendritic cells,,,)

Question 7

describe the outcome of thymic education

Answer 7

1. central tolerance
   - T cells which do not react to their body’s own peptide antigens are selected. if T cells were not educated, they could attack the bodys own cells causing autoimmune rxns
2. T cell diversity in peptide recognition
   - T cells will recognise any non-self peptide, provided it is presented by their wn MHC molecule on an antigen presenting cell
3. maturation of T cells

Question 8

describe how B cells are educated within the bone marrow

Answer 8

• in the bone marrow, self antigen is presented on stromal cells
• if B cells respond to self antigen through their B cell receptors, the interaction leads to apoptosis or receptor editing (re arrangement of BCR genes to avoid self recognition)
• educated naive B cells express both IgD and IgM on their cell membrane

Question 9

how do B cells recognise a huge diversity of antigens

Answer 9

• the specificity of a particular antibody is determined by the shape of its variable region
• while still at the B cell progenitor stage in the bone marrow, B cells rendomly rearrange their variable , diversity and joining genes
• diversity comes from the fact that there are multiple copies of the V, D and J genes that can be joined together in different combinations

Question 10

how do T cells recognise a huge diverstiy of antigens

Answer 10

• the specificity of a particular T cell receptor is determined by the shape of its variable region
• while still at the T cell progenitor stage in the thymus, T cells randomly rearrange their variable, diversity and joining genes
• diversity omes from the fact that there are multiple copies of the V, D and J genes that can be joined together in different comibination

Question 11

what does MHC class I display on healthy cells

Answer 11

host cell peptide (self)

Question 12

which CD4/CD8 phenotype is characteristic for helper T cells

Answer 12

CD4+/CD8-

Question 13

which CD4/CD8 phenotype is characteristic for Cytotoxic cells

Answer 13

CD8+/CD4-

Question 14

what is the order of CD4/CD8 expression in the development progenitor T cell => cytotoxic T cell

Answer 14

CD4-/CD8- => CD4+/CD8+ => CD4-/CD8+