Immune system development


The child's immune system is an intricate network of interdependent cell types, substances, and organs that collectively protect the body from bacterial, parasitic, fungal, viral infections, and tumor cells.


The immune system was not recognized as a functional unit of the body until the late twentieth century, probably because its parts are not directly connected to each other and are spread in different parts of the body.

Organs of the immune system

The immune system contains the following organs and cells: tonsils and adenoids; the thymus gland; lymph nodes; bone marrow; and white blood cells that leave blood vessels and migrate through tissues and lymphatic circulation. The spleen, appendix, and patches of lymphoid tissue in the intestinal tract are also parts of the immune system.

The essential job of this system is to distinguish self-cells from foreign substances and to recognize and take protective action against any materials that ought not to be in the body, including abnormal and damaged cells. The immune system can seek out and destroy disease germs, infected cells, and tumor cells. The immune system includes the following cells:

  • T lymphocytes (T cells)
  • B lymphocytes (B cells)
  • natural killer cells (NK cells)
  • dendritic cells
  • phagocytic cells
  • complement proteins

These cells develop from "pluripotential hematopoietic stem cells" starting from a gestational age of about five weeks. They circulate through various organs in the lymphatic system as the fetus develops. T and B lymphocytes are the only units of the immune system that have antigen-specific recognition powers; they are responsible for adaptive immunity. In other words, the T and B cells are important in the immunity that vaccination promotes.

How immunity works

The lymphatic system is a key participant in the body's immune actions. It is a network of vessels and nodes unified by the circulatory system. Lymph nodes occur along the course of the lymphatic vessels and filter lymph fluid before it returns to the bloodstream. The system removes tissue fluids from intercellular spaces and protects the body from bacterial invasions.

Types of immunity

Immunity is the ability of the body to resist the infecting agent. When an infectious agent enters the body, the immune system develops antibodies which can weaken or destroy the disease-producing agent or neutralize its toxins. If the body is re-introduced to the same agent at a later time, it is capable of developing antibodies at a much faster pace. As a result, the individual would likely not become sick, and immunity has developed.

Natural immunity is present when a person is immune to a disease despite not having either the disease itself nor any vaccination against it. Acquired immunity may be either active or passive. Active immunity comes from having the disease or by inoculation with antigens, such as dead organisms, weakened organisms, or toxins of organisms. The antigens introduced during vaccination produce antibodies that protect the body against the infecting agent, despite the fact that the person does not become sick. Passive immunity is relatively short lived and is acquired by transferring antibodies from mother to child in the uterus or by inoculation with serum that contains antibodies from immune persons or animals. Passive immunization is used to help a person who has been exposed or is already infected to fight off disease. Although various types of serums may be used to produce passive immunization, gamma globulin is the most frequently used source of human antibodies.

Development of the immune response

Normal infants have the capability to develop responses to antigens at birth. Infants also start life with some immunoglobulin antibodies acquired from the mother. These antibodies cross the placental barrier, but not all types are transmitted equally. In particular, infants start with antibodies to viruses and gram-positive organisms, but not to gram-negative organisms. Gram is the name of a stain that distinguishes broad classes of bacteria. Gram-negative organisms are responsible for many diseases, including gonorrhea, pertussis (whooping cough), salmonella poisoning, and cholera. Escherichia coli (E. coli) is another common gram-negative organism.

Immunoglobulin antibodies are divided into five classes. The capacity of the body to produce each immunoglobulin varies with age. Newborn babies (premature and full-term) begin to synthesize antibodies at an increased rate soon after birth in response to antigenic stimulation of their new environment. At about six days after birth the serum concentration of specific antibodies rises sharply, and this rise continues until adult levels are achieved by approximately the end of the first year. Maternal immunity gradually disappears during the first six to eight months of life. A concentrated level of antibodies is reached and maintained by seven to eight years of age.

Common problems

Persistent infections

One of the greatest strains on the immune system is an infection it cannot remove. Parents should pay attention to unexplained fevers; night sweats; or tender, swollen lymph nodes. These symptoms can signify a hidden infection or cancer . Infections of the mouth and gums as well as sexually transferred infections often go unnoticed while they drain the vitality of the immune system.

Indiscriminate use of antibiotics

When the immune system successfully controls an infection on its own, it becomes stronger and better able to handle future threats. Antibiotics are powerful medicines that should be given only when the immune system cannot contain a bacterial infection. Overuse of antibiotics may cause the body to breed new strains of antibiotic-resistant or more dangerous bacteria. In the long run, overuse of antibiotics weakens the immune system.

Misuse of immunosuppressive drugs

Immunosuppressive drugs used in cancer chemotherapy or to suppress rejection of organ transplants are necessary. Of greater concern is the widespread use of corticosteroids or steroid derivatives used to treat allergies , autoimmune diseases, and inflammatory conditions. Though sometimes necessary, these drugs cripple the immune response and are often misunderstood, abused, and over-prescribed.

Radiation and hazardous chemicals

Exposure to radiation and hazardous chemicals may also damage the immune system. Excessive radiation of diagnostic x rays of the neck and chest may damage the thymus gland behind the breastbone. The thymus gland is an integral part of the immune system.

Blood transfusions and injections of blood products

Blood transfusions and injections of blood products may broadcast viral diseases like hepatitis that stress the immune system by flooding it with foreign proteins. In an emergency it may not be possible to do without blood transfusions. Sources of blood and blood products are regulated and screened for infectious substances and were as of 2004 much safer.

Other factors

Certain factors have damaging effects on the immune system of infants. Excessive consumption of alcohol during pregnancy leads to depressive levels of vitamin B and zinc, which are essential to immune competence. Alcoholism can also reduce the uptake of several other important nutrients needed for neonatal immune systems. Prolonged stress during pregnant and in breastfeeding mothers reduces the effectiveness of the immune system as well as the quality of immunologic factors in breast milk.

Cigarette smoking raises the white blood cells count, activating the immune system; however, smoking causes low-grade chronic bronchitis , low birth weight infants, and weakened natural immunity in newborns. Infants and children constantly exposed to cigarette smoke have weakened immune systems.

Toxic points—areas of localized infections such as dental abscesses or infected tonsils—may disturb the normal neutralization and weaken the cellular defenses in pregnant mothers and in children.

Deficiencies of many nutrients, especially certain vitamins and minerals , may weaken the immune system. Excessive exercise may depress the immune system temporarily.


Autoimmunity occurs when the immune system mistakenly attacks the body's own tissues, resulting in disease that can be mild or severe. Common autoimmune disorders are rheumatoid arthritis, glomerulonephritis, rheumatic fever , and systemic lupus erythematosus (SLE). Autoimmune reactions may be set off by infection, tissue injury, or emotional trauma in people with a genetic tendency to them.

Parental concerns

Parents may be concerned that children with acute illnesses have compromised immune systems and are less likely to have a positive response to vaccines or may be more likely to develop adverse reaction to the vaccine than healthy children. Parents may also believe that children who are ill should not further burden an immune system already committed to fighting an infection.

Most pediatricians would agree that there should be a delay in vaccinations for children with severe illnesses until the symptoms of illness are gone. The reason for deferring immunization is to avoid superimposing a reaction to the vaccine on the underlying illness or attributing symptoms of the underlying illness to the vaccine by mistake. However, a low-grade fever or cold is not a contraindication for routine vaccinations.

Parents may also be concerned that the many different vaccines that infants are given may overwhelm a child's immune system. However, infants have the capacity to respond to large numbers of antigens. Parents who worry about the increasing number of recommended vaccines may take comfort in knowing that children are exposed to fewer antigens in vaccines as of the early 2000s than in previous decades. Two reasons account for this decline: the worldwide elimination of smallpox and advances in protein chemistry in vaccines with fewer antigens.

Vaccines may cause temporary suppression of delayed-type hypersensitivity skin reactions or alter certain lymphocyte function tests. However, the short-lived immunosuppression caused by certain vaccines does not result in an increased risk of infections from other pathogens soon after vaccination.


Antibody —A special protein made by the body's immune system as a defense against foreign material (bacteria, viruses, etc.) that enters the body. It is uniquely designed to attack and neutralize the specific antigen that triggered the immune response.

Antigen —A substance (usually a protein) identified as foreign by the body's immune system, triggering the release of antibodies as part of the body's immune response.

Corticosteroids —A group of hormones produced naturally by the adrenal gland or manufactured synthetically. They are often used to treat inflammation. Examples include cortisone and prednisone.

Immune system —The system of specialized organs, lymph nodes, and blood cells throughout the body that work together to defend the body against foreign invaders (bacteria, viruses, fungi, etc.).

Immunization —A process or procedure that protects the body against an infectious disease by stimulating the production of antibodies. A vaccination is a type of immunization.

Lymphocyte —A type of white blood cell that participates in the immune response. The two main groups are the B cells that have antibody molecules on their surface and T cells that destroy antigens.

Phagocytosis —A process by which certain cells envelope and digest debris and microorganisms to remove them from the blood.



Burney, Lucy. Boost Your Child's Immune System: A Program and Recipes for Raising Strong, Healthy Kids. New York: Newmarket Press, 2005.

Janeway, Charles. Immunobiology: The Immune System in Health and Disease. New York: Garland Publishing, 2004.

Parham, P. The Immune System. New York: Garland Publishing, 2004.


Offit, Paul A. "Addressing Parents' Concerns: Do Multiple Vaccines Overwhelm or Weaken the Infant's Immune System?" Pediatrics 109 (January 2002): 124.

Aliene Linwood, RN, DPA

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