What is the role of helper T cells in the adaptive immune response?

A.Helper T cells activate B cells and cytotoxic T lymphocytes to kill infected host cells.

B.Helper T cells deactivate B cells and cytotoxic T lymphocytes to kill infected host cells.

Diagram showing the activation of B cells by helper T cells
Diagram showing the activation of B cells by Helper T cells

The correct answer is A. Helper T cells activate B cells and cytotoxic T lymphocytes to kill infected host cells.

Humans depend on having a well functioning immune system in order to stay healthy. We are constantly exposed to harmful bacteria and viruses every day, and without a good system in place, we would not live very long.

The immune system has carefully evolved to detect and kill any foreign entities that may enter our bodies. The human immune system is comprised of many different cells that provide defense against invading pathogenic microbes.

Some of the types of immunity are non-specific while others are specific. These specific forms of immunity are known as the adaptive response. Adaptive immunity relies on specialized white blood cells that work together in concert to find and destroy invading microbes.

There are two types of specific immune reactions to microbes that occur, the humoral response and the cell-mediated response. The humoral response involves B lymphocytes which develop into plasma cells that secrete antibodies in response to the antigens of microbes.

The T cells bring about what is known as the cell-mediated response. Antigen-presenting cells trigger the helper T cells of the system. These then trigger the B cells to produce antibodies and the cytotoxic T cells to secrete chemicals to kill the invading organism.

Furthermore, the helper cells also trigger the activity of macrophages which ingest particles by phagocytosis.

Immunity

Immunity is crucial to the survival of an organism, and it is a well-known fact that diseases in which the immune system is attacked are particularly deadly for people.

For example, the rare genetic disorder severe combined immunodeficiency is very deadly because the development of the cells of the adaptive immune system is flawed, so individuals are extremely susceptible to infection.

The HIV virus also severely compromises the immune system and causes much disability and many deaths every year.

Our bodies are exposed to pathogenic organisms all the time, and to survive we have to have a strong immune system that can fight off this continual invasion of microbes.

The human immune system has the capacity to ‘remember’ exposure to pathogens, which helps us as we become older. This is why children are sick more often as adults; they have not had as much time to develop an immunological memory to common microbes.

It is therefore relatively common for young children to be sick quite often compared with older children and adults. Babies also acquire some protection from the mother while in the uterus and when passing through the birth canal at birth.

Adaptive immunity

The human immune system has several divisions including being categorized into nonspecific and specific responses. The specific immunity is accomplished by cells of the adaptive immune system.

The adaptive immune system can be further subdivided into a cell-mediated and humoral immune response. The cell-mediated response involves the activity of highly specialized cells that each plays a role in destroying pathogenic organisms that have invaded the body.

The humoral response also includes special cells, but in this case, the cells secrete chemicals called antibodies that destroy invaders.

There are several types of white blood cells (leukocytes) that are involved in the immune response of the body. Two of the main cell types are T lymphocytes and B lymphocytes.

The B lymphocytes are the cells that are tasked with bringing about the humoral immune response. These cells get their name from the presence of B type proteins on the plasma membrane.

They are able to secrete proteins known as antibodies in response to specific antigen proteins that occur on a particular pathogen.

All the lymphocytes originate from stem cells that are present in the bone marrow, and then they develop further into their respective forms.

The B cells differentiate further in the bone marrow to form plasma cells which are then capable of secreting antibodies to bring about a humoral response.

The T lymphocytes and macrophages

The T cells of the immune system are also produced in the bone marrow, after which they usually migrate to the thymus where they differentiate and mature into their respective types. They are named for the presence of a T protein on the cell membrane.

There are many different types of T lymphocytes that have different roles in bringing about cell-mediated immunity in the body. One of the most important of these cells is the helper T cell.

This cell is important in initiating the immune response and it not only activates B cells but also the cytotoxic T cells. The helper T cell is able to do this by secreting chemical messages that then activates the appropriate cell.

These helper cells are themselves activated by special antigen presenting cells in the body. In addition to the T cells and B cells that the helper cells activate, they also trigger the action of macrophages.

These are white blood cells that ingest foreign particles by the method of phagocytosis. Macrophages also help trigger T cells by presenting them with the antigens of pathogens that they have ingested.

The cytotoxic T cells are also known as CD8+ cells, and they work by directly killing pathogenic microbes by means of the chemicals that these T cells produce.  These cells often target cells that have been invaded by a virus, or cells that have turned cancerous.

Another important type of T lymphocyte is the regulatory T cell. This cell helps to reduce the immune response. These lymphocytes really work in conjunction with helper cells to carefully control the cell-mediated and humoral immune response.

References

  1. Editors of Encyclopedia Britannica (2018). T cell. Retrieved from Encyclopedia Britannica.
  2. Editors of Encyclopedia Britannica (2018). B cell. Retrieved from Encyclopedia Britannica.
  3. MF Flajnik, M Kasahara (2010). Origin and evolution of the adaptive immune system: genetic events and selective pressures. Nature Reviews Genetics.
  4. S Perdue, JH Humphrey (2018). Immune system. Retrieved from Encyclopedia Britannica.
  5. B Alberts, A Johnson, J Lewis, et al. (2002). Molecular Biology of the Cell, 4th edition. New York: USA, Garland Science.

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