Assignment No. 2

BT302 IMMUNOLOGY

FALL 2021

Total Marks: 10

Due date: 3^rd January 2022

QUESTION:

1. List down the differences between innate and adaptive immune systems. (5 marks)
2. What are antibodies? Explain the types of it and describe how they are produced in the body in case of infection? (5 marks)

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  1. List down the differences between innate and adaptive immune systems. (5 marks)

 

Answer:

Difference between Innate and Adaptive Immunity

Innate immunity is something already present in the body. Adaptive immunity is created in response to exposure to a foreign substance.

 

S.N.	Characteristics	Innate Immunity	Adaptive immunity
1.	Presence	Innate immunity is something already present in the body.	Adaptive immunity is created in response to exposure to a foreign substance.
2.	Specificity	Non-Specific	Specific
3.	Response	Fights any foreign invader	Fight only specific infection
4.	Response	Rapid	Slow (1-2 weeks)
5.	Potency	Limited and Lower potency	High potency
6.	Time span	Once activated against a specific type of antigen, the immunity remains throughout the life.	The span of developed immunity can be lifelong or short.
7.	Inheritance	Innate type of immunity is generally inherited from parents and passed to offspring.	Adaptive immunity is not passed from the parents to offspring, hence it cannot be inherited.
8.	Memory	Cannot react with equal potency upon repeated exposure to the same pathogen.	Adaptive system can remember the specific pathogens which have encountered before.
9.	Presence	Present at birth	Develops during a person’s lifetime and can be short-lived.
10.	Allergic Reaction	None	Immediate and Delay hypersensitivity
11.	Used Against	For microbes	Microbes and non-microbial substances called antigens
12.	Memory	No memory	Long term memory
13.	Diversity	Limited	High
14.	Speed	Faster response	Slower response
15.	Complement system activation	Alternative and lectin pathways	Classical pathway
16.	Anatomic and physiological barriers	Skin, Mucous membranes, Temp, pH, chemicals, etc.	Lymph nodes, spleen, mucosal associated lymphoid tissue.
17.	Composition	The innate immune system is composed of physical and chemical barriers, phagocytic leukocytes, dendritic cells, natural killer cells, and plasma proteins.	Adaptive immune system is composed of B cells and T cells.

 

2. What are antibodies? Explain the types of it and describe how they are produced in the body in case of infection? (5 marks)

 

Answer:

Antibodies

Antibodies are Y-shaped proteins that bind to the body's foreign invaders and signal the immune system to get to work. Antibodies are specialized, Y-shaped proteins that bind like a lock-and-key to the body's foreign invaders — whether they are viruses, bacteria, fungi or parasites.

Types

• This isoform accounts for 70–75% of all human immunoglobulin’s found in the blood. ...
• IgM is the largest antibody and the first one to be synthesized in response to an antigen or microbe, accounting for 5% of all immunoglobulin’s present in the blood. ...
• ...
• ...
• ...
• Camelid antibodies

IgG

This isoform accounts for 70–75% of all human immunoglobulins found in the blood. Depending on the size of the hinge region, the position of disulfide bonds, and the molecular weight of the antibody, IgG can be further divided into 4 subclasses: IgG1, IgG2, IgG3, and IgG4.In general, proteins are responsible for triggering IgG1 and IgG3 production, whereas IgG2 and IgG4 typically respond to foreign polysaccharides. IgG is the main component of the humoral immune system (immune response initiated by macromolecules present in the extracellular fluid) because of its abundance.Due to its small size (monomeric) and high diffusibility, IgG is the prevalent type in the extracellular fluid that binds Fc receptors on phagocytic or other lytic cells and initiates the antibody-dependent cell-mediated cytotoxicity (ADCC) response – a cell-mediated defense mechanism wherein effector cells (phagocytes) destroy the target cell.In addition, IgG triggers phagocytosis to initiate opsonization reaction – a process used to destroy foreign particles (e.g. bacteria) through phagocytosis. Apart from these functions, IgG is the only antibody that can cross the placenta and provides passive immunity to the fetus and infants in the first few months of life.

IgM

IgM is the largest antibody and the first one to be synthesized in response to an antigen or microbe, accounting for 5% of all immunoglobulin’s present in the blood. IgM typically exists as polymers of identical subunits, with a pentameric form as the prevalent one. In its pentameric form, five basic antibody units are attached by disulfide bonds. Other forms include secretory IgM, which is synthesized by glandular-associated B cells, and monomeric form, which is present in the B cell membrane and functions as a B cell antigen receptor. Due to its large size, IgM is mostly intravascular and has a lower affinity for antigens. However, since pentameric IgM has 10 antigen binding sites, it has higher avidity (overall binding strength) for antigens than IgG and acts as an excellent activator of the complement system and agglutination.

IgA

It accounts for 10–15% of all immunoglobulin’s and is prevalent in serum, nasal mucus, saliva, breast milk, and intestinal fluid. It has two subtypes namely IgA1 and IgA2, which mainly differ in terms of their hinge region characteristics. At mucosal surfaces, IgA provides the primary defense against inhaled and ingested pathogens.

IgE

IgE is the least prevalent one, with a serum concentration 10,000 times lower than IgG. However, the concentration of IgE increases significantly in allergic conditions, such as Broncho pulmonary aspergillosis, and parasitic diseases, such as schistosomiasis.

In response to pathogens, IgE binds to mast cells via specific receptors, followed by pathogen-mediated cross-linking of these receptors (degranulation). This causes recruitment of eosinophil at the site of infection and destruction of pathogens via ADCC-type mechanisms.

IgD

IgD functions as a B cell antigen receptor and may participate in B cell maturation, maintenance, activation, and silencing. Although the exact function is still unclear, IgD may be involved in humoral immune responses by regulating B cell selection and homeostasis.

Camelid antibodies

Camelid (single-domain) antibodies, commonly known as nanobodies, are composed of only heavy chains (no light chains). These antibodies were discovered in 1989 following the analysis of total and fractionated IgG molecules in the serum of a camel.In Camelid antibodies, the antigen recognition site is composed of a single variable domain. These antibodies are potential candidates to be used in antibody-based therapies because of some special characteristics, such as smaller size, good solubility, high thermostability, high affinity and specificity, low immunogenicity, and higher tissue penetration rate.

Produced in the body in case of infection

Humoral Immunity: Virus and/or virus-infected cells can stimulate B lymphocytes to produce antibody (specific for viral antigens) Antibody neutralization is most effective when virus is present in large fluid spaces (e.g., serum) or on moist surfaces (e.g., the gastrointestinal and respiratory tracts).

The first antibodies to be produced in a humoral immune response are always IgM, because IgM can be expressed without isotype switching (see Figs 4.20 and 9.8). These early IgM antibodies are produced before B cells have undergone somatic hypermutation and therefore tend to be of low affinity.

 

 

 

 

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