This document contains lecture notes on major histocompatibility complex (MHC) and related topics from a biotechnology course. It discusses antigen-presenting cells, the structure and function of MHC class I and II molecules, similarities and differences between the two classes, MHC-associated genes, and important immune signaling molecules like cytokines, interleukins, interferons, and chemokines. Diagrams are included to illustrate MHC pathway and types of interferons. The notes provide an overview of key concepts in MHC and immunology for students in the biotechnology course.

1. MHC
19 July 2021 Abhijit Debnath BP605T and Biotech Unit-1 1
CO1.1
Noida Institute of Engineering and Technology
(Pharmacy Institute) Greater Noida
Abhijit Debnath
Asst. Professor
NIET, Pharmacy
Institute
Unit: 3
Subject Name: Biotechnology
(BP605T)
Course Details
(B. Pharm 6th Sem)

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 Antigen-presenting cells
 Major Histocompatibility Complex (MHC)
 Structure Of MHC
 MHC Working Pathway
 MHC Associated Genes
 Similarities Between MHC Class I & MHC Class II
 Differences Between MHC Class I & MHC Class II
 Cytokines
 Interleukins (IL)
 Interferons (IFN)
 Chemokines
Lecture 20
Noida Institute of Engineering and Technology
(Pharmacy Institute) Greater Noida

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ANTIGEN-PRESENTING CELLS
 Antigen-presenting cells (APCs) are a group
of immune cells that mediate the cellular
immune response by processing and
presenting antigens for recognition by
certain lymphocytes such as T cells. Classical
APCs include dendritic cells, macrophages,
Langerhans cells and B cells.
MHC

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ANTIGEN-PRESENTING CELLS

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MAJOR HISTOCOMPATIBILITY COMPLEX
 Major histocompatibility complex (MHC), group of
genes that code for proteins found on the surfaces of
cells that represent antigen to T cells for intracellular
recognition & discriminate between self (our cells
and tissues) and nonself (the invaders or modified
self).
 Another function of the major histocompatibility
complex is tissue allorecognition, an important factor
in the prevention of successful organ transplantation.
 In human beings the complex is also called the
human leukocyte antigen (HLA) system.
 There are two major types of MHC protein
molecules— MHC class I and MHC class II.
The B-cell receptors (antibodies) can recognize
antigens and on their own, while T-cells can do so
through the mediation of MHC.
MHC

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STRUCTURE OF MHC
MHC Class I molecules are found on almost all the nucleated cells of
the body.
MHC Class I molecules are found on almost all Antigen Presenting
cells like macrophages, B cells and dendritic cells.
MHC Class I MHC Class II

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MHC WORKING PATHWAY
MHC Class I MHC Class II

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 In humans, the MHC proteins are encoded by a cluster of genes located on chromosome 6.
 The MHC gene family is divided into three subgroups: MHC class I, MHC class II, and MHC class III.
 Among all those genes present in MHC, there are two types of genes coding for the proteins MHC class I molecules and
MHC class II molecules that directly involved in the antigen presentation.
MHC ASSOCIATED GENES

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SIMILARITIES BETWEEN MHC CLASS I & MHC CLASS II
 Both are synthesized in rough endoplasmic reticulum
 Both are found on the surface of APC surface
 Both are encoded by genes in HLA locus
 In both class I and class II, expression of genes is co-
dominant
MHC Class I MHC Class II

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DIFFERENCES BETWEEN MHC CLASS I & MHC CLASS II
MHC Class I MHC Class II
MHC Class I MHC Class II
Peptide binding
domain
alpha1, alpha2 alpha1, beta1
Amino Acids Have 8-10 amino acids Have 13-18 amino acids
Distribution All nucleated cells All Antigen Presenting cells like macrophages, B
cells and dendritic cells.
CD4 binds to the
b2 region
a1 and a2 domains a1 and b1 domains
Present antigen to cytotoxic T cell lymphocytes Present antigen to helper T cell lymphocytes
Binding site for T
cell co-receptor
CD8 binds to the a3 region CD4 binds to the b2 region
Binds with Bind endogenous antigens synthesized in a cell Binds exogenous antigens
Acts Presence of foreign or over-abundant antigens
targets cell for destruction
Presence of foreign antigens induces antibody
production, and attracts immune cells to area
of infection
Chain Has no invariant chain Has invariant chain

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Cytokines
Small soluble molecules

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CYTOKINES
* Autocrine mean cytokine acts on the same cell and para line means cytokine acts on the nearby cells
 Cytokines are produced and secreted by wide variety of cells
 They act as Intercellular mediators hormone-like substances that
means they are signaling molecules
 Cytokines are soluble molecules and some of them are membrane
bound molecules
 Chemically they can be protein or glycoprotein
 The molecular mass is less than 30 kDa
 Cytokines have short half-life
 Mostly cytokine act over a short distance (autocrine or paracrime) *
 Cytokines are effective at low concentrations this is because of the
specific high affinity cytokine receptors

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CYTOKINES
 Cytokines Strom in Covid-19

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Important cytokines which are involved in signaling between cells of the immune system are
 Interleukins (IL)
 Interferons (IFN)
 Chemokines
CYTOKINES

15.  Interleukins are a subset of a larger group
of cellular messenger molecules called
cytokines, which are modulators of cellular
behaviour.
 Like other cytokines, interleukins are not
stored within cells but are instead secreted
rapidly, and briefly, in response to a
stimulus, such as an infectious agent.
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INTERLEUKINS (IL)

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INTERLEUKINS (IL)
Courtesy: Frank Lectures

17.  A virus-infected cell releases interferons causing nearby cells to heighten their anti-viral defenses.
 Interferons (IFNs) are proteins made and released by host cells in response to the presence of pathogens such as
viruses, bacteria, parasites or tumor cells.
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INTERFERONS (IFN)
 IFNs belong to the large class of proteins known as cytokines, molecules
used for communication between cells to trigger the protective
defenses of the immune system that help eradicate pathogens
 They also allow for communication between cells to trigger the
protective defenses of the immune system that eradicate pathogens or
tumors.
 ϒ-IFNs are produced by NK cells that activate macrophages (Type II IFNs) NK cells ϒ-IFNs Macrophage activation
 Whereas, α and β IFNs are produced by virus infected cells that activate NK cells. (Type I IFNs) Virus infected cells α, β
IFNs NK cellactivation.

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Courtesy: Frank Lectures
INTERFERONS (IFN)

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TYPES OF INTERFERONS

20.  Chemokines, are a family of small, secreted, and structurally related cytokines with a crucial role in inflammation and
immunity.
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CHEMOKINES
 They are also key mediators of cancer
related inflammation being present at
tumor site for pre-existing chronic
inflammatory conditions but also being
target of oncogenic pathways
 Play role in determining the
composition of tumor stroma, they
were found able to directly affect
cancer cell proliferation and metastasis

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Courtesy: Frank Lectures
CHEMOKINES

22. THANK YOU