Lymphocyte Development and Diversity Flashcards
cells that are generally identical, descending from the same cell
clones
- in the context of b and T cells, clones are cells that have the exact same antigen receptor and antigen specificity
the process by which an antigen will find the right lymphocyte (B or T cell) that recognizes it and binds to it out of the pre-existing cell pool of differing antigen specificities - leading to reproduciton of that specific lymphocyte to fight the infection
clonal selection
After clonal selection, binding signals mitotic division and proliferation of the cell.
the specific chosen lymphocyte will divide and multiple - now we have a large army of adequate size to fight off the microbe
clonal expansion
group of cells with secretory granules, they include neutrophils, basophils and eosinophils
granulocytes
types of leukocyte
what are the two types of lymphocytes?
B cells & T cells
*located in blood/tissue
B cells- make antibodies
T cells - include CD4+ (helper) & CD8+ (Killer)
where do all blood cells come from?
all blood cells descend from the hematopoietic stem cells (HSC) in bone marrow
- are ‘self-renewing’ - they make one identical cell and one that is differentiated down a pathway - committed to making all various blood cells
2 pathways:
‣ one pathway leads to a megakaryocytes which leads to platelets (impt for clotting), red blood cells (delivery of oxygen), monocytes-> macrophages & dendritic cells, neutrophils
◦ another precursor cells is the common lymphoid progenitor cell (CLP) -> B cells -> antibodies and other pathway to T cells (CD8 &CD4)
B cell maturation occurs all in bone marrow except for the last step when immature b cells leave bone marroe to final differentiation step into mature B cell which happens in the …..
lymph/spleen
T cell origination also begins in the bone marrow but then moves right to the … where maturation begins
thymus in the chest
HSC -> CLP -> Pro T cell (migration to thymus in chest) -> cell goes thru lots of division to one that makes TCR beta chain (pre T cell) -> CD4+ & CD8+ T cell receptor cells (expresses both 4 & 8 on surface -> final maturation is development of cells that are either CD4 or CD8
these are transmembrane proteins that bind to peptides and display them to T cells on their surface
(bc T cells can only recognize peptides unlike antibodies that can see everything)
MHC - major histocompatibility complex
Why do we need T cells?
- T cell could recognize peptide on surface of infected cell, and could ignore cloud of virus above cells unlike antibodies
- T cells can only recognize peptide-MHC complexes displayed on the surface of cells “billboard” proteins
- better for dealing with virally infected host cells
- T cells are uniquely capable of recognizing infected cells, ignoring cloud of virus
We have so many different antibodies and receptors coming from limted number of genes. What contributes to this large diversity?
Genes have Combinatorial diversity and junctional diversity
Antibodies have a constant C terminal side that doesnt change and an N terminal side that does change
The N terminal side has the V(D)J segments that make up the antibody and T cell receptor genes
*
V(D)J recombination is the genetic shuffling process that generates receptor diversity
◦ In theory, any given D segment can combine with any given J segment, then these two segments can combine with any given V segment. This is called V(D)J recombination.
this describes the DNA sequence variations introduced by the improper joining of gene segments during the process of V(D)J recombination (genetic shuffling) and from the addition of nucleotides to the sequence at splice sites
Junctional diversity
diversity of antibody genes generated by the random formation of many different VJL and VDJH combinations
combinatorial diversity
