B-Cells vs T-Cells
(Similarities and Differences between B-Lymphocytes and T-Lymphocytes)
Lymphocytes are the key cells of the immune system and they are responsible for the adaptive immune response of an organism. They are also responsible many of the immunological characteristics such as specificity, diversity, memory and self/non-self recognition. Lymphocytes constitute about 20 – 40% of the body’s White blood cells and 99% of the cells of the lymph. Lymphocytes are broadly classified into THREE populations based on their function, lifespan, cell surface components and most importantly their place of maturation. They are B-Lymphocytes (B-Cells), T-Lymphocytes (T-Cells) and Natural Killer Cells (NK Cells).
They mature in the bone marrow or bursa (in birds). B-cells possess membrane bound immunoglobulins which acts as the receptors for the antigens. They are involved in the humoral (antibody mediated) immune responses.
Learn more: Cell Mediated vs Humoral Immunity
They mature in the thymus, hence the name. T-cells possess receptors for antigens on their surface but it is structurally different from immunoglobulins. They are involved in Cell-mediated immune responses.
The present post discusses the Similarities and Differences between B-Lymphocytes (B-Cells) and T-Lymphocytes (T-Cells) with a Comparison Table.
Structure and Functions of Immunoglobulins (Antibodies)
The Organization of Heavy and Light Chains in an Immunoglobulin (Ig)
In the previous post, we have discussed the introductory features of antibodies. There we have also discussed the reason for calling Antibodies (Ab) as Immunoglobulins (Ig). In this lesson, we will see the detailed molecular structure and organization of immunoglobulins (antibodies).
What are Immunoglobulins (Ig)?
As we discussed earlier, the Antibodies or Immunoglobulins are globular proteins present in the serum and tissue fluids. They are produced by the plasma cells (B-cells) and are used in the immune system of the body to neutralize pathogenic microbes or other toxic foreign components.
Antibodies play a very crucial role in the immune system of an organism. Antibodies bind to definite molecules of microbes called antigens with high affinity and specificity. This enables our immune system to detect foreign organisms such as invading pathogens, of its products and initiate the mechanism to eliminate these foreign particles. The production of antibodies by the plasma cells is also stimulated by the antigens.
How Immunoglobulins (Ig) are classified?
The immunoglobulins constitute about 20 – 25% of the total serum proteins. Based on the Physiochemical and Antigenic differences, the immunoglobulins are classified into FIVE categories. These immunoglobulins variants are called as Isotypes. The five isotypes or classes of the immunoglobulins are given below.
Antibodies vs Immunoglobulins
(Why are Antibodies called as Immunoglobulins?)
All Antibodies are Immunoglobulins but all Immunoglobulins are NOT Antibodies.
Antibodies are the antigen binding proteins found on the B-cell membrane and secreted by the plasma cells of the immune system. Antibodies are commonly called as ‘IMMUNOGLOBULINS’. In the present post we will see, what is the exact difference between an Immunoglobulin and an Antibody, and also why antibodies are called immunoglobulins?
What are Antibodies?
Ø Antibodies are globular proteins (globulins) present in the serum and tissue fluids.
Ø They form one of the major components of the blood plasma proteins.
Ø In the blood, three types of globulin proteins are present and they are named as alpha (α), beta (β) and gamma (γ) globulins.
Ø All antibodies are gamma (γ) globulins.
Ø Antibodies confer protection against microbial pathogens and, they act as the first line defense against infections.
Ø Antibodies are highly specific and they specifically bind to foreign particles called antigens.
Ø The antibodies can protect us from the invading microbes in four different ways:
1. They can prevent the attachment of microbes to the mucosal surface of the host.
2. They reduce the virulence of the pathogen by neutralizing the toxins and viruses.
3. They facilitate phagocytosis by opsonization of microbes.
4. They can activate the complement system.