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13.6.3. Immunodeficiency

Immunodeficiency

The immune deficiency is the inability to develop an adequate immune response to the presence of antigens strangers, but not be disposed of properly.

We will distinguish between congenital and acquired immunodeficiencies.

Congenital immunodeficiencies

These immunodeficiencies are inherited, so you are born with them.

Normally, they are caused by defects in B lymphocytes, which cannot produce enough antibodies. They can also be due to failures in the synthesis of the proteins that make up the complement  or to malfunction of T lymphocytes.

If the problem is not being able to produce antibodies, the abnormalities appear after six months of life, when most of the IgG from the mother have been lost during pregnancy or through the placenta .

If the problem is in nonspecific immunity or is related to T lymphocytes, immunodeficiency phenomena can appear from the moment of birth.

Children with congenital immunodeficiency syndrome are called "bubble children" because they must live in a sterile room and avoid contact with people, animals, or objects that carry germs. One solution is bone marrow transplantation, capable of forming immunocompetent cells.

Acquired immunodeficiencies

The acquired immunodeficiencies are more frequent than congenital immunodeficiencies. They appear as a consequence of some factors such as leukemia, radiation exposure, long treatment with immunosuppressants, ... or by serious diseases that weaken the immune system.

One of the most serious immunodeficiencies is AIDS (acquired immunodeficiency syndrome), produced by HIV (human immunodeficiency virus), which attacks and destroys T helper lymphocytes (TH). The body is defenseless against antigens and tumor cells, so the affected person can have significant infections and develop some types of cancers.

An individual is said to be seropositive when he has antibodies in his blood against the HIV virus. The cells that HIV infects are mainly T4 or helper lymphocytes.

As we saw, HIV is a retrovirus, so it has RNA (not DNA) as its genetic material. Specifically, it has two equal strands of single-stranded RNA. Its capsid is icosahedral and has a lipoprotein envelope.

AIDS development

AIDS develops as follows:

  1. HIV enters the body of a healthy person from an infected person. The virus is found in the blood and other body fluids such as semen and vaginal secretions. The main transmission mechanisms are: When the virus reaches the circulatory system of the new host, it binds to T4 (THlymphocytes. The union is made between a specific virus coat protein (Gp 120) and the CD4 receptor protein of T4 lymphocytes, thanks to a specific recognition between both molecules. Binding with macrophages can also occur.
    1. Directly through blood, through transfusions, or through contaminated syringes.
    2. Through sexual intercourse in which semen or vaginal secretions come into contact with micro-wounds or erosions through which the virus can enter.
    3. From mother to child, usually during pregnancy or delivery.
  2. Fusion of the virus envelope with the lymphocyte cell membrane occurs, and the virus's RNA and reverse transcriptase enzyme penetrate the lymphocyte cytoplasm.
  3. Thanks to reverse transcriptase (a DNA polymerase), double-stranded DNA is formed from RNA, which is incorporated into the T4 lymphocyte genome and constitutes a provirus, so that its DNA, integrated into cellular DNA, is transmitted to daughter cells each time the lymphocyte divides. There is also a slow multiplication of the virus, which is released by budding. Lymphocytes do not suffer immediate damage, but they do suffer in the long term .
  4. At a certain point, the infected T4 lymphocytes die, and the decrease in their number causes immunodeficiency . If there are less than 150 T4 lymphocytes per mm3 of blood (in a healthy person there are 500 / mm3), the immune deficiency is serious and death occurs due to opportunistic infections, such as pulmonary tuberculosis and pneumonia, among others. Rare tumors such as Kaposi's sarcoma, which affects the blood capillaries of the skin, are also common.

It occurs since the infection by HIV until it appears the AIDS usually a time ranging from 5 to 10 years. First there is an asymptomatic phase (lasts from months to years), but in the blood plasma of these people there are antibodies against HIV, they are seropositive people, who can spread the disease.

AIDS treatment

Although an effective treatment for AIDS is not yet available, the combination of drugs currently used slows the progression of the syndrome, although it does not succeed in eliminating the virus and, therefore, a cure is achieved. The drugs used interfere with reverse transcriptase, with the binding of the virus to T4 lymphocyte receptors or with the protease enzyme , which allows the correct formation of the virus capsid.

Currently, the only effective way to control the spread of AIDS is through information campaigns to avoid high-risk situations and behaviors that favor the transmission of the virus.