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BIOC39H3 Chapter Notes -Neutrophil, Lysosome, Histocompatibility

Biological Sciences
Course Code
Bebhinn Treanor

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Some background knowledge:
- in bone marrow, pluripotent HSC give rise to common lymphoid progenitor cells
- can produce either TC or BC
those CLPC that develop into precursor cells that’re commited to become BC
what distinguishes 1 precursor from another
is cell-surface markers
- ex. CD34 present on all human HSC
pro-B cells: earliest identifiable cells in BC
- type of progenitor cell
- retain limited capacity for self-renewal
- divide to produce both more pro-B BC and cells
that will go onto develop further
- main event in pro-BC stage: reararngement of
HC genes, which always comes before LC gene
- early pro-B cell stage: joining of D_H and J_H
gene segments
- late pro-B cell stage: joining of V_H segment to
rearranged DJ_H
- rearranged gene is transcribed through to mu
C-region gene, the nearest C gene to rearranged
V region; RNA transcript is spliced to produce
mRNA for the mu heavy chain first type of Ig
chain made by developing BC
- after BC expresses mu chain, its called pre-B
- pre-BC
- represent 2 stages in B-C development:
- 1. Large-pre BC: less mature; have successfully rearranged HC
gene and make mu chain; stopped rearrangements of HC genes but haven’t
started rearrangement for LC genes
- after it has rearranged HC successfully and made mu chain, it
matures into small-pre BC.
- 2. Small-pre BC: more mature; LC gene rearrangement occurs in

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- kappa LC genes first to rearrange; if these rearrangements fail to make viable
kappa chian then lambda LC genes rearranged
- when successful joining of LC V and J segment achieved, LC protein synthesized
& assembled in ER with mu chains to form membrane-bound IgM
- IgM furhter associates with Ig-alpha and Ig-beta for form functonal BCR complex
then transported to cell surface;
- rearrangement of light-chain genes stops and small-preBC becomes IMMATURE
Adaptive immune response: response of antigen-specific B and T lymphocytes to antigen,
including the development of immunological memory
Adaptive immunity: state of resistance to infection that is produced by adaptive immune
- body’s 3rd line of defence
- iniitated only after physical barriers have been breached and innate immune reponse failed to
get rid of invading pathogen
- two types of lymphocyte: B cell and T cell
- unique featue: able to distinguish from one specific pathogen to another
- enables body to make more focused and forceful reponse to any pathogen than is
possible with innate immune response alone
3-1 Innate and Adaptive immunity differ in their strategies for pathogen recognition
- innate immune receptors recognize either structures shared by many different pathogens or
alterations to human cells that’re commonly induced by presence of pathogens

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adaptive immune response
- BC and TC recognize pathogens by using cell surface receptors of just one molecular type:
B-cell receptors: antigen receptor on B cells, which is a membrane-bound
immunoglobulin molecule. Each BC programmed to make a single immunoglobulin
type. The cell-surface form of immunoglobuin serves as BCR for specific antigen.
Associated in the membrane with the immunoglobulin are the signal transduction
molecules Ig-alpha and Ig-beta
- can bind to vast variety of different chemical structures
T-cell receptors: highly variable antigen receptor of TC’s; on most TC’s it is composed
of variable alpha chain and variable beta chain and is known as alpha:beta TCR;
recognizes peptide antigens derived from breakdown of proteins. On minority of TC’s.
variable chains are GAMMA and DELTA chains gamma-delta TCR;
- recognize more limited range of antigens than BCR
- only expressed as cell-surfaced, and never as soluble proteins (Contrast: antibody for BCR)
- type of antigen it reocgnizes is less well-defined
- both types of receptors present at cell surface in association with the complex of
invariant CD3 chains and X chains, which have a signalling function
- can be in an almost infinite number of different versions, each with binding site for different
- on infection with pathogen, only those lymphoctes with receptors that can bind to components
of particular pathogen are selected to divide, proliferate and differentiate into effector
lymphocytes (FIGURE 1.10)
- evolved only in vertebrates
- suggests that its evolution became feasible or advantageous only with degree of
cellualr and anatomical complexity attained by vertebrates
- advantages
1. strong immune respones can be precisely targetted aagainst particular pathogen
2. some of the pathogen specific BC’s and TC’s that prolfierate during first infection are
retained long afte rinfection terminated; enables subseqeuent infectiosn by same pathogen to be
countered and terminated promptly with less disease immunological memory - what
vaccinations seak to induce
3. gives the slowly evolving vertebrates a response that can keep up with multiplicity of
rapidly evolving microbes, ebcause it has capacity and versatility to recognize and attack any new
3-2 Immunoglobulins and TCR’s are highly variable recognition molecules of adaptive
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