Adaptive Immune System: 5 Reasons Why Adaptive immune System is Superior to Innate Immunity

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The adaptive immune system has for a long time been believed to be superior to the innate immune system. Is it true? We shall answer this question by saying everything known about the adaptive immune system. Then, we make the conclusion credibility of this claim.

The adaptive immune system is also known as the specific immunity or the acquired immune system. This immune system is specific because unlike the innate immune system (Which attacks broad categories of pathogens) it mounts a very specific immune response to each antigen. Antigens can be pathogens or non-infectious proteins like tumors.

Branches of the Adaptive Immune system

Your adaptive immune system is divided into two branches. These include the cell-mediated branch and the humoral branch.

1. Cell-mediated immunity

This branch is mediated by the T cells. The T cells include three important subsets. We have the T-helper lymphocytes (CD4+), Cytotoxic lymphocytes (CD8+), and the T-regulatory cells The last subset is differentiated from T-helper cells by being CD25+ and FOXP3+.

The role of the T cells in the immune system is analogous to that of a cornerstone of a house or the pillars of a storey building. We all know that those pillars are the ones that maintain the integrity of the building. This analogy underscores the importance of T cells in the immune system. Let’s explore further to understand what they do.

Recognition of Antigens by T cells

The T cells start their development in the bone marrow and complete it in the thymus. From the thymus T cells are released into the peripheral circulation as naïve T cells.  All T cells have a T cell receptor (TCR) that they use to specifically bind to antigens. For it to be functional, the TCR is further associated with a surface protein called CD3. This protein helps in signal transduction into the cell.

Therefore, for T cells to recognize antigens, the antigens must be presented to them by the antigen-presenting cells (APCs) – including the macrophages, dendritic cells, and B cells.

The recognition of the antigen is deemed to have happened when APC through major histocompatibility molecules (MHC) presents a peptide/antigen to the T cell’s TCR. This is referred to as signal 1. But for the T cells to become effector cells, we must have signal 2. Signal 2 involves interaction between CD28 on the T cells and B7 molecules (B7-1 or CD80 and B7-2 or CD86) on the surface of the APCs.

Effector function of T cells

At this point, the T cells have now been activated and they can become effector cells or memory T cells. The T cells will differentiate into TH1 or TH2 subsets which are differentiated by the type of cytokines they produce.

Examples of cytokines produced by TH1 cells include interferon-gamma, tumor necrosis factor, and IL-2 while TH2 examples include IL-4, IL-5, and IL-10. These cytokines have far-reaching effects on an immune response which is why we say these cells are like pillars of a house.

While the CD4+ T-helper cells recognize antigens presented by MHC class II, the CD8+ T cells recognize those presented in the context of MHC class I. The effector cytotoxic T cells then unleash their cytotoxic granules to kill cells (e.g., virally-infected cells and Tumor cells).

Do you remember the T regulators cells (T regs) that we had mentioned as the third subset? The T regs downgrade the activities of both T-helper cells and cytotoxic cells once an attacking antigen has been eliminated to prevent autoimmunity. Autoimmunity is a situation where the immune cells attack your own cells which is a highly undesirable outcome. It can also be very dangerous.

2. Humoral Immunity  

This branch is mediated by antibodies which are produced by the B cells. The B cells begin their development in the liver and mature in the bone marrow. Mature B cells are those with a B cell receptor (BCR).

Recognition of Antigens by B cells

The B cells recognize antigens when those antigens bind to the BCR in a very specific way. A signal is transduced into the cell for that cell to further develop into a plasma cell or a memory B cell.

Effector Function of B cells

After binding to the antigens through BCR, your B cells will become effector cells or memory cells. The antigen-bound B cells mature to become plasma cells which are the antibodies-producing cells. The plasma cells do not proliferate further. They only produce antibodies. You can also have memory plasma cells in your body.

Reasons Why Adaptive is Superior to Innate Immune System

There have been arguments why the adaptive immune system has been regarded as superior to the innate immune system. Let us now see the reasons here:

1. The adaptive immune system keeps the memory of all the antigens it has encountered. That means that subsequent response to the same antigens is fast and more robust. On the other hand, the innate immune system does not maintain any memory of what it has encountered before.

2. Your adaptive immune system can be manipulated scientifically to confer long-lasting protection through vaccination and immunization.

3. Your adaptive immune system is highly specific in its response to antigens while the innate immune system is non-specific in the sense that it responds to broad categories of antigens that have pathogen-associated molecular patterns (PAMPs).

4. The adaptive immune system is highly diverse and customizable meaning that it can deal with any type of antigens that it could ever encounter. The innate immune system on the other hand is rigid in the sense that its receptors are encoded in the germline and cannot adapt to a new type of antigens whose specificity is not pre-existing

5. Adaptive immunity (i.e., humoral antibodies) is transferrable from one animal to the other through what is referred to as passive immunization. This practice is not possible with innate immunity.

Conclusion

The adaptive immune system is superior to the innate immune system. However, the two arms of the immune system work collaboratively to eliminate unwanted antigens in your body. With a completely defective adaptive immune system, one is unlikely to live because they would be too vulnerable to infections. 

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