The cells of the immune system can be categorized as lymphocytes (T-cells, B-cells and NK cells), neutrophils, and monocytes/macrophages. These are all types of white blood cells. The major proteins of the immune system are predominantly signaling proteins (often called cytokines), antibodies, and complement proteins.

1. Cells of the
Immune System
Amandeep Singh
Assistant Professor
Department of Biotechnology
GSSDGS Khalsa College Patiala

2. Introduction
Lymphocytes are one of many types of white
blood cells (WBCs) produced in the bone marrow
by the process of hematopoiesis.
The two major populations of lymphocytes—
B lymphocytes (B cells) and T lymphocytes (T
cells).

3. B lymphocytes (B cells)
• B lymphocytes (B cells) originate and mature in the
bone marrow.
• Derived their name from Bursa of Fabricus (in Birds).
• Mature B Cells have surface receptors for Antigens
known as B cell receptor.
• This B-cell receptor (BCR) is a membrane bound
antibody molecule.
• There are approximately 1.5x105 molecules of BCR on
the surface of single B cell.
Naïve B Cell
+
Antigen Activated B Cell

4. Naïve B Cell
+
Antigen Activated B Cell
Proliferation
Differentiation
Plasma Cell Memory Cell
Inactive but matured B
cell that have not
encountered with
antigen yet.
Antibodies
Humoral Immunity
&

5. T lymphocytes (T cells)
• T lymphocytes (T cells) derived their name from the site of their
maturation.
• T cells although produce in bone marrow but mature in Thymus.
• Unlike B cells, T cells do not recognize free antigens.
• Antigen must be displayed together with MHC molecules on the
surface of Antigen Presenting Cell (APC) or on virus infected
cells, cancer cells, graft.
• All T cells possess T cell receptors (TCR).
Two types of T Cells:
• Helper T-cells (TH cells)
• Cytotoxic T-cells (TC cells)

6. Types of T Cells
T cells displaying CD-4 (cluster of differentiation) on the surface = TH Cell
T cells displaying CD-8 (cluster of differentiation) on the surface = TC Cell
TC CellTH Cell
CD-4 interact with MHC-II present on APCs
CD-8 interact with MHC-I present on all nucleated cell
MHC = Major Histocompatibility complex and its function is antigen presentation.

7. Rule of 8 to Remember MHC & CD
Relationship
MHC CDX = 8
I
II
=
=
8
8
X
X
8
4
APC T-cell

8. Natural Killer Cells
• Granular lymphocytes
• Show cytotoxic activity against tumor cells and virus-infected cells
They recognize target in 2 ways:
1. Check abnormalities
a) Reduction in number of
MHC-I on the cell surface
b) Unusual profile of surface
antigens displayed by
tumor cells or virus
infected cells

9. 2. By binding to antiviral antibodies attached to virus infected cells by CD-16 receptors

10. Chediak Higashi Syndrome
• Autosomal recessive disorder.
• In people having impairment with neutrophils,
macrophages and NK cells.
• Mice with autosomal mutation ‘Beige’ lack NK cells.
This making their body more susceptible to tumor.

11. Mononuclear
Phagocytes
Granulocyte monocyte
progenitor cell
Pro-monocyte
Blood
Remain for
8 Hours Enlarge
Tissue
Monocyte
Bone marrow
Dendritic cell
Macrophage

12. Types of Macrophages
Free/wandering Fixed
Alveolar macrophages in lungs
Histocytes in connective tissues
Kupffer cells in liver
Mesangial cells in kidney
Microglial cells in brain
Osteoclasts in bones

13. Granulocytic Cells

14. Neutrophils Eosinophils Basophils Dendritic Cells
Multi-lobed nucleus Bi-lobed nucleus Single lobed nucleus Act as APCs
Stained with both acidic
and basic dyes
Stained with acidic dye-
eosin red
Stained with basic dye-
crystal violet, methylene
blue
Express high level of
MHC-II
Phagocytic cells Phagocytic cells Non-phagocytic cells
Potent APC than B-cells
and macrophages
First to arrive at the site
of inflammation
Defense against
parasitic organisms
Major role in allergic
responses
Leukocytosis: Increase
in neutrophils, indicator
of infection
Mast cells work together
with basophils