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What is the humoral immune response?

An immune response mediated by macromolecules (antibodies).


When does class changing occur?

after the generation of diversity (maturing of the B cell). Occurs during immune response based on what the antibody needs to act against.


What part of the BCR protein determines class/isotype? What part determines the specificity? How does the B cell change the class/isotype?

The constant part of the BCR determines its class, the variable part determines its specificity. The B cell can change class by using mRNA splicing on the constant part of the BCR gene.


What is clonal selection?

Clonal selection refers to the process by which lymphocytes which recognise antigens during an immune response are stimulated to undergo cell division, the selective expansion of unique lymphocyte clones.


How does clonal selection occur?

Lymphocytes capable of binding to antigens or antigen peptides take up the atigen with high efficency (assuming the antigen is highly present e.g in an infection). The antigen specific B or CD8+ T cells then process and present the antigen on MHC-II to helper T cells with the right T cell receptors which will then provide the antigen presenting cells with cytokines. Leading to clonal selection into plasma cells and a small number of memory B cells in the case of B cells or Cytotoxic T cells and a small number of memory T cells in the case of T cells. Note that they also require their second signal (need to become activated). Once the antigen is gone from the system the lymphocytes will no longer be able to supply antigen peptides to CD4+ and hence will not recieve cytokines


What are memory cells similar to? How do they differ?

Memory cells are similar to naive cells of the same type, they persist for years in the blood and lymphatic tissue and express antibody only as B cell receptor and don't secrete antibody (making them similar to naive B cells) but differ as they will respond rapidly if the antigen returns as they don't require cytokines from the CD4+ T cells to become the activated state (e.g plasma cells in B cells).


What is a primary immune response characterised by?

An immune response which takes roughly 7-14 days before enough antibody has been produced to eliminate the pathogen, has a relatively low amount of antibody, mainly in the form of IgM.


What is a secondary immune response characterised by? What does this allow us to make?

A secondary immune response relies on memory B and T cells. It acts quickly, within 2-3 days because sufficent antibody and T cell action occurs to eliminate pathogens, main antibody is IgG. This immune response is the basis of vaccines.


If we give a patient antigen A what immune response will they experiment? What if we then give them antigen A and B 3 months later?

A primary immune response will occur against A the first time, when both A and B are present a secondary immune response will occur against A and a primary immune response will occur against B.


What is a common cytokine released by CD4+