Constitutes 20 – 40 % of the body’s white blood cell and 99 % cells in the lymph. Circulate continuously in the blood and lymph and migrates into the tissue spaces. On the basis of function and cell membrane component, mainly 3 types :- B cells, T cells and NK (Natural killer cells)

1. Presented By,
Jyoti Prakash sahoo
Roll No. – 14 - AMJ – 15
Deptt. Of Agril. Biotech.
AAU, Jorhat
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Lymphocytes
September 10, 2015

2. What are these?
 Constitutes 20 – 40 % of the body’s white blood cell and 99 % cells in
the lymph.
 Circulate continuously in the blood and lymph and migrates into the
tissue spaces.
 On the basis of function and cell membrane component, mainly 3
types :- B cells, T cells and NK (Natural killer cells)
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September 10, 2015

3. B cells
 B cells or B lymphocytes are a type of lymphocyte in the humoral
immunity of the adaptive immune system.
 B cells can be distinguished from other lymphocytes, such as T cells
and natural killer cells (NK cells), by the presence of a protein on the B
cell's outer surface known as a B cell receptor (BCR) or
Immunoglobulin (Antibody).
 This specialized receptor protein allows a B cell to bind to a specific
antigen.
 In birds, B cells mature in the bursa of Fabricius (the name of "B" cells
comes from the name of this organ).
 In mammals, immature B cells are formed in the bone marrow.
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September 10, 2015

4.  Generally large “Y” shaped glycoproteins (they
have bound carbohydrates – sugars) of molecular
weight around 150,000.
 There are five structural types (classes) of
antibodies in humans based on this Y-shaped
motif, these are IgA, IgD, IgE, IgG, and IgM, where
Ig stands for Immunoglobulin.
 Consists of four polypeptide (protein) chains (two
heavy chains and two light chains) connected by
disulphide bonds. These chains have several
domains.
Immunoglobulins (Antibodies)
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September 10, 2015

5. What happens when B cell encounters the antigen
(Effector Cells)
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September 10, 2015

6.  They can be distinguished by the presence of a T-cell receptor (TCR)
which is a unique antigen binding molecule on the cell surface.
 They are called T cells because they mature in the thymus (although
some also mature in the tonsils).
 T cell receptors only recognize antigen that is bound to the cell
membrane protein called MHC (Major Histocompatibility Complex).
 when a antigen combined with an MHC molecule on a cell, the T Cell
differentiated into effector T cells and memory T cells.
T Cells
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September 10, 2015

7.  It is a set of cell surface molecules encoded by a large gene family which controls a major part
of the immune system in all vertebrates.
 The major function of major histocompatibility complexes is to bind to peptide fragments
derived from pathogens and display them on the cell surface for recognition by the
appropriate T-cells.
MHC (Major histocompatibility complex )
Heavy chain
polypeptide domains
Non-covalently
associated light chain
Heterodimers
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September 10, 2015

8.  T helper cells (TH cells) assist other white blood cells in immunologic processes, including
maturation of B cells into plasma cells and memory B cells, and activation of cytotoxic T cells
and macrophages type of white blood cell that engulfs and digests cellular debris, foreign
substances, microbes.
 These cells are also known as CD4+ T cells because they express the CD4 glycoprotein on
their surfaces.
 These cells differentiate into effector cells that enable activation of B cells, TC cells.
Helper T Cell
Activation of a helper T cell and its roles in immunity:
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9.  Cytotoxic T cells (TC cells, or CTLs) secrete cytotoxin which triggers destruction of the
pathogen's DNA or perforin which is a protein that creates holes in the pathogens plasma
membrane. The holes cause the pathogen to lyse (rupture).
 These cells are also known as CD8+ T cells since they express the CD8 glycoprotein at their
surfaces.
Cytotoxic T Cell
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September 10, 2015