The Composition of the Human Immune System

A normal immune system is the basic condition for human health. Many diseases ( such as lupus erythematosus, rheumatoid arthritis, Behcet's disease, xerosis, etc.) are often related to immune dysfunction. In recent years, the incidence of various immune diseases has gradually increased, and immunotherapy methods have emerged as the times require, allowing people to see the hope of curing some difficult-to-conquer diseases .

The composition of the human immune system

First of all, we need to understand the composition of the human immune system. The immune system is a very important system. Like other major systems in the human body, it is composed of many different cells. Immune cells, normally present in large numbers in our blood, make up a bulk of the blood in the blood system.

In addition to red blood cells, platelets, etc., the cells in the blood are all components of the immune system ( including macrophages , neutrophils , dendritic cells, natural killer cells , T lymphocytes , B lymphocytes, etc. ) .

Among them, the most important family of immune cells is lymphocytes, including B lymphocytes, T lymphocytes and NK lymphocytes. B lymphocytes, actually the rocket army, launch missiles, inhibit the infection of germs, and clear the germs, which is humoral immunity .T lymphocytes rely on cellular immunity to function . B lymphocytes and T lymphocytes were discovered by American scientist Max Cooper and Australian scientist Jack Miller. The two scientists won the Lasker Basic Medicine Award in 2019 at the same time.

Antiviral immune response

In infection, B cells and T cells play different roles. Let’s talk about T cells first, which are usually divided into two categories. The first category is CD4+ T cells , which function to produce cytokines, also known as helper T cells (Th) . The second type is CD8+ T cells , whose function is to produce cell lytic enzymes, also known as killer T cells (CTL) , responsible for attacking virus-infected cells and tumor cells.

What are the roles of lymphocytes in immune response and immune response? After the virus invades the human body, how the human immune system recognizes, functions, and eliminates the virus has been relatively in-depth understanding. The immune response is divided into two stages. The first stage is the response stage of innate immunity. The human body will produce a large amount of interferon in the early stage of virus infection . The characteristics of this stage: it comes quickly, and it begins to appear 1 to 2 days after the virus is infected; but it also goes away quickly, and it has dropped to a low point in 5 to 6 days, and the specificity is not strong. In the innate immune response stage, no matter what kind of virus invades, it is the same procedure, and it does not care about the specificity of the virus, nor can it produce a good immune agent.

In the second stage, B cells and T cells are mainly responsible. This stage is also called adaptive immunity . Max Cooper discovered that: the antibodies produced by B cells can prevent viruses that invade the human body from further infecting human cells, and can recognize and bind extracellular viruses. Antibody immune response, also known as humoral immunity, mainly eliminates extracellular viruses ; effector T cell immune response, also known as cellular immunity, mainly eliminates cells that have been infected by viruses . Therefore, the immune system can recognize and clear the virus in two different places.

Another characteristic of B cells and T cells is that antibodies and T cells continue to exist after infection, which forms "immune memory". Immunological memory is a specificity. For example, after the human body is infected by influenza, the number of antibodies and T cells against influenza will increase, so the human body can be immune to some viruses for life.

Immunological memory is the immunological basis for the development of various vaccines . If the specific B cells and T cells of the human body are activated by the vaccine, they can be pre-stored in the human body for a long time, so that a relatively long-term protection can be formed, and human beings can obtain protection and immunity without direct infection with the virus.

Tumor Immune Cell Therapy

Using the immune system to fight tumors is the dream of immunologists. In 2013, the American Journal of Science officially listed immunotherapy as the fourth formal treatment for cancer besides surgery, radiotherapy, and chemotherapy .

Dr. Steven A. Rosenberg of the American Cancer Research Center is a pioneer in exploring immune cell therapy for cancer. He found that there are a large number of tumor infiltrating lymphocytes (TILs) in tumor tissues . He called these T cells Take it out of the body to amplify it, and then infuse it back to the patient, and found that it has a better effect.

Based on this principle, Professor Carl H. June of the University of Pennsylvania further created CAR-T cell therapy, which uses lymphocytes in the peripheral blood of tumor patients instead of tumor-infiltrating lymphocytes to give these T cells plus CAR (Chimeric Antigen Receptor) can accurately identify tumor cells in the blood. This therapy has been successful in treating leukemia.

In terms of solid tumors, the 2018 Nobel Prize was awarded to two immunologists, American immunologist James P Alison and Japanese immunologist Tasuku Honjo , who considered how to use immune System to resist tumors and help cancer patients to cure tumors. These two scientists advocate immune checkpoint (such as PD-1 and CTLA-4, etc.) blockade therapy, which is a clinical trial in the treatment of melanoma.

As you can see from the diagram, the blue line of one of the drugs shows that it has a cure rate of about 20% for patients, and the red line is this drug plus another drug, which is a combination of two drugs. For these tumor patients with advanced melanoma, about 60% of the patients can be completely cured and can prolong their survival for more than three years, which shows that immune checkpoint blockade therapy or immunotherapy can help some patients with advanced tumors recover completely . This type of therapy is continuously being developed and clinically tested in countries around the world.

Autoimmune disease

However, anything in the world is always too much. Abnormal immunity or hyperimmunity (such as rheumatoid arthritis, GVHD, transplant rejection and hypersensitivity) are problems within the immune system (immunity hyperactivity or immune dysregulation) that affect people's health and quality of life.

With the continuous development of immunology, drugs are also constantly evolving. One class of drugs stands out, which targets cytokines secreted by immune cells (cytokines are communication channels for immune cells to communicate with each other, just like we communicate through WeChat) . If the function of these molecules is blocked, the immune system will go out of control, the communication between immune cells will be blocked, and the inflammatory response can be alleviated.

There are many immune cells that can produce cytokines. Th cells specialize in regulating immune responses and inflammatory diseases by secreting cytokines. Among them, Th2 is the main regulator of allergic diseases. Drugs targeting Th2 have achieved relatively great success in the treatment of allergic diseases. In addition to Th1 and Th2, Th17 (T helper cell 17, Th17 for short) and Tfh (T follicular helper cell, Tfh for short) were discovered in the past 20 years, and Dong Chen’s laboratory also participated in the work . In 2008, antibody drugs against IL-17 began to enter the clinic, and were officially approved in 2015, and my country has also approved them. The indications are some diseases of dermatology and rheumatology , such as psoriasis (commonly known as psoriasis) , psoriatic arthritis, and ankylosing spondylitis of rheumatology. At present, these drugs are very effective in the treatment of psoriasis and can basically be cured. With the continuous development of immunology and the deepening of immune research, we have more and more knowledge about immune regulation and immune mechanism, which can also help explain some clinical diseases, and more importantly, develop some new drugs to treat them All kinds of immune diseases can also use our immune system to help us better resist infectious diseases and tumors.