Major histocompatibility complex Flashcards
(31 cards)
what is needed for an appropriate response to a foreign antigen?
lymphocytes must recognise antigens to be stimulated to divide and differentiate
what does each lymphocyte have?
its own antigen specificity
what initates a primary response?
recognition and binding to an antigen by a specific lymphocyte
What does the primary response produce?
- Effector cells- job to eliminate antigen
- memory cell pool
Describe the role of the memory cell pool.
- Long lived and still specifc to antigen
- Gone through one round of activation so during second encounter to the same antigen there is a faster and greater response which produces more effector cells and a larger memory cell pool
what is antigen recognition on B cells mediated by?
surface immunoglobulin
what is antigen recognition on T cells mediated by?
T cell receptor (TCR)
what do T cells only recognise?
antigens that are expressed on cell surfaces
where can antigens expressed on cell surfaces be derived from?
- These antigens can be derived from pathogens that replicate within host cells e.g. viruses or intracellular bacteria
- Alternatively these antigens may come from pathogens or their products that have been endocytosed from the extracellular fluid
In both T and B cell cases, what do cells display on their surface?
peptide fragments derived from the pathogen’s proteins
what can be detected by T cells?
presence of infected cells and foreign antigens
what is major histocompatibilty complex (MHC) ?
Specialised glycoprotein that delivers pathogen-derived peptides and presents them at the cell surface
where are MHC proteins encoded for?
large cluster of genes on chromosome 6
what happens when MHC antigens on transplanted tissue are recognised by recipient’s immune system?
rejection
what are MHC molecules also refereed to as?
HLA- human leucocyte antigens
what does T cells recognise ?
combination of MHC molecule and small peptide fragment of antigen
what are the 2 MHC families?
- class I
- class II
what are the 3 members of Class I?
HLA-A, HLA-B and HLA-C
what are the 3 members of Class II?
HLA-DP, HLA-DQ and HLA-DR
what makes each class distinct?
distinct subunit compositions but similar three-dimensional structures
where is class I expressed?
expressed on all nucleated cells including leucocytes
where is class II expressed?
expressed only on leucocytes which present antigen to T cells e.g. monocytes, marcophages
what does each individual express?
two forms of each protein co-dominantly - one derived
from the mother, one from father
What are clinical implications of MHC?
- Tissue grafting e.g. kidney transplants, skin grafts
- Certain HLA types are predisposed to certain diseases
- Forensic medicine
