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Humoral Immunity

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What is Humoral Immunity?

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The immune system provides protection to our bodies from possibly harmful substances by identifying and responding to antigens. Antigens are foreign substances (usual proteins) that are present on the surface of viruses, fungi, cells, or bacteria. Antigens could also be certain non-living substances such as chemicals, toxins, drugs, and a few foreign particles like a splinter. An antigen elicits an immune response when the immune system tries to destroy the antigen.

When our bodies get invaded by any virus, parasites, or bacteria, it sets off an alarm that starts a chain of reactions resulting in cellular activities within our immune systems. Our innate immune cells like dendritic cells, basophils, or neutrophils may get deployed for attacking the pathogen’s invasion. Most of the time these cells are enough to do the job of destroying the invader.

In this article, we will look into what the innate immunity of human bodies is,  what is humoral immunity, the difference between humoral and cell mediated immunity, and humoral immunity steps. You could also download humoral immunity ppt to refer to it at your convenience.

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What is Innate Immunity?

Innate immunity (also called nonspecific immunity) is the defence system we are all born with which protects us against all antigens. 

  • Innate immunity is the first line of defence in the immune system. It is that barrier that keeps harmful substances from entering our bodies. Some examples of innate immunity are:

  • Cough reflex

  • Mucus that traps bacteria and small particles.

  • Enzymes are present in skin oils and tears.

  • Skin

  • Stomach acid

  • But at times our bodies need a more sophisticated attack which is performed by B-cells and T-cells which are special ops of the immune system. This line of defence utilizes past interactions and behaviours to identify particular foreign threats and counteract them when these threats reappear. The T cell and B cell are part of our adaptive immune system.

  • After the primary immune response fails to handle the pathogen, the adaptive immune system causes a secondary immune response. This is called acquired immunity and it is of two types: humoral and cell mediated immunity responses.

  • The humoral immune system is also termed antibody mediated immunity and comes in protein chemical form.

  • Some of the examples of humoral immunity are substances like interferon, interleukin-1 (which causes fever), and the body’s complement system.

  • The humoral immune system is based on serum antibodies produced by plasma cells. The serum binds to the antigen to assist in their elimination from our bodies.

  • Humoral immunity protects the extracellular spaces of the body. Extracellular space is where most pathogens invading our bodies multiply. Hence it is an important place to destroy antigens.

Humoral and cellular immunity are two different types of adaptive immunity. Adaptive immunity produces an immune response that is antigen-specific. During an adaptive immune response, the antigen gets identified through receptors present in lymphocytes. Then immune cells clones are produced for attacking that particular antigen.

The main difference between humoral and cell mediated immunity is that in humoral immunity antibodies specific to the antigen are produced whereas in cell-mediated immunity no antibodies are produced but it uses apoptosis to destroy infected cells.

Difference Between Humoral Immunity and Cell Mediated Immunity

Humoral Immunity

Cell-Mediated Immunity

Humoral immunity uses B cells to secrete antibodies that move around in the blood as a soluble protein.

Cell-mediated immunity occurs through the activation of antigen-specific T cells.

The antibodies created by humoral immunity act on extracellular microbes and their toxins.

This immune response acts on intracellular microbes for example bacteria, viruses, tumour cells, and parasites.

BCRs (B Cell Receptor) are involved in this.

TCRs (T Cell Receptors) are involved in this.

The accessory receptors in humoral immunity are Igɑ, Igβ, CD21, Cd40, and Fc.

The accessory receptors in cell-mediated immunity are integrins, CD2, CD4, CD3, CD28, and CD8.

In this response, antibodies are secreted by plasma B cells.

Here T cells secrete cytokines.

This does not act on transplants and tumour cells.

This acts on transplants and tumour cells.

Humoral Immunity Steps

The diagram below depicts the stepwise functioning of the humoral immunity system:

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  • The first step in the humoral immunity process is the activation of B cells once an antigen is recognized.

  • The antigen is then engulfed and digested by the B cells.

  • The fragments of the antigen are then displayed on the surface of B cells which attract the T helper cell.

  • The T helper cell binds to the B cell at the site of the antigen and releases cytokines.

  • The cytokines signal the B cell to develop into a plasma cell..

  • These secreted antibodies lock onto the matching antigens forming antigen-antibody complexes. These antigen-antibody complexes are cleared by the liver, spleen, or complement cascade.

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FAQs on Humoral Immunity

1. What are plasma cells?

When B cells get activated they form plasma cells, which are antibodies factories. Antibodies are large proteins in the shape of the letter Y. Antibodies recognize and bind to antigens. Plasma cells produce many copies of a single type of antigen. The antibodies travel all through the body in lymph and blood and each antibody can bind to just one type of antigen. When an antibody binds with an antigen it forms an antigen-antibody complex which flags the cell which contains the antigen for destruction by phagocytosis.

Most of the plasma cells have a very short lifespan of just a few days, though some of them can live much longer than that (some might survive even the lifetime of an individual). Plasma cells that live longer are called memory cells since they retain the memory of a specific pathogen even after the infection is gone for a long time. These memory cells help in launching a rapid response if the same pathogen invades the body again.

2. What is apoptosis?

Apoptosis is a controlled and regular mechanism involved in the growth of an organism. It is also referred to as PCD or Programmed Cell Death which results in characteristic changes in the cell and eventually death. Another term of apoptosis is cellular suicide since cells take part in its death. 

  • The balance of cell multiplication is maintained by apoptosis. The whole process of apoptosis is regulated by specific proteases known as caspases.

  • The process of apoptosis follows a well-defined series of morphological changes:

i. The plasma membrane of the cell bulges

ii. The cell dries and shrinks

iii. The nucleus gets fragmented.

iv. Condensation of chromatin occurs

v. Lastly, the chromosomal DNA becomes fragmented.

  • Apoptosis affects cell membrane, nucleus, mitochondria, and cytoplasm. 

  • When apoptosis occurs, the cellular contents do not get released into the extracellular environment.

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