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Lecture 13

BIOL103 Lecture 13: Week 5, Lectures 13-15

Course Code
BIOL 103
Virginia K Walker

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Week !
B"Cellular Immune Response
These cells# unlike the B cells# mature in the thymus and are therefore called T
Many of the cellular components in blood# including T$lymphocytes# originate
in the bone marrow
T cells
Have a T receptor
A dimer with an alpha and beta polypeptide chain $ containing
variable and constant regions
The constant membranes have a transmembrane
The amino acid sequence in the variable regions di%er
in di%erent clones of T cells
Each variable region is encoded by various variable#
diverse and joining “gene pieces” and is assembled to
the constant region $ which is anchored to the
membrane and does not change

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T cell receptor assembly (do not need to know)
Can never be transcribed
Cut randomly
An enhancer attaches
Alpha and beta pair come soon a&er biosynthesis to form the receptor
Two di%erent Cbeta (CB' and Cb() regions encode a transmembrane
Cannot bind an antigen unless they also bind to MHC
The Major Histocompatibility Complex
Also known as the Human Leukocyte Antigen (HLA)
This is a bad name# because they do not have to be on leukocytes when
talking about humans
Cellular “identity tags” that are genetic markers of self
MHC I is found on most cells in the body
Exception: erthrocytes (RBCs or platelets $ need a nucleus?)
Binding is stabilized by CD) (on the killer T cells * cytotoxic cells)
MHC II is found only on antigen$presenting cells such as macrophages (or
presentation cells)# B cells and a few other immune system cells
Binding is stabilized by CD+ (on helper T cells)

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Displayed like a barcode on the outside of a cell on its membrane !
• Cell$mediated Immunity
Macrophage/dendritic cell/ antigen presentation cell (APC) come frome
Are binded by virgin T cells
Contain foreign antigen
Antigen carried to the membrane by the MHC protein
Drags foreign antigen to the surface
Thought to look like a hot dog in a bun
MHC II interaction is stabilized by a cluster determinant glycoprotein (CD+)
As soon as it binds# the cell is induced to divide via a signal transduction event
mediated by cytokinesis
Helper T cells
Stay in circulation for a long time
Memory T cells
Have same antigen specificity for antigen receptors
Four Functions of the helper T cells
'" The helper T cell binds to an APC (macrophage)
Provides signal of infected cell
Binding releases a chemical signal
Peptide hormone cytokine * interleukin# IL
Controversy on calling them hormones
Stimulates mitotic division of the helper T cell
Sometimes called the T+ cell
MHC II interaction is stabilized by CD+
Creates clonal population of helper T cells
• Identical# have same specificity in T cell receptor
(" The helper T cell binds B cells bearing a B cell receptor and a bound
When bound# interleukin is released which stimulates the B cells to
divide and produce a clonal population of B cells resulting in more
plasma B cells and the synthesis of specific antibodies
-" The helper T cell produces cytokines which stimulate killer T cells
(cytotoxic T cells) to attack “infected” cells
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