The immune system is the body’s defense mechanism to fight against germs and prevent infections in the body. Whenever the body’s immune system is overcome, a germ be it a virus or bacteria or fungus can lodge within the body and lead to infection.
A normal healthy individual can also get infections. However, serious repeated infections may suggest that there is something wrong with the child’s immune system and that may be leading to repeated serious infections.
Immune system consists of skin, the nose and airway cells and finally various white blood cells (WBCs) in the blood. The skin is the most important barrier for infection. An intact skin prevents entry of most of the germs and any break in the continuity of the skin can lead to infection. Thus, infections are commonly seen in patients with burns.
Our next most common defense mechanism is the airway passages through which we breathe. The air which we breathe may contain plenty of germs and if they were not captured and expelled from the body would lead to different types of infections. The air passages contain a special type of hair called the cilia and also have mucus lining it. Thus any germ is trapped in the mucus and by beating of the cilia is moved upward towards the mouth and expelled out by the cough mechanism. Thus, these 2 most important barriers prevent most of the infections in the human body.
However, if a germ bypasses these 2 defense mechanisms then there are certain cells in the blood (WBCs) that fight these germs. These cells consists of specialized cells called as neutrophils, T lymphocytes, B lymphocytes and monocytes. B lymphocytes also release certain proteins called as antibodies that fight against most of the bacteria. There are 5 major types of antibodies – IgA, IgG, IgE, IgD and IgM. T lymphocytes fight against mainly viruses and fungi.
Thus, any defect in these specialized cells can lead to defective immunity and immune deficiency disorders that may lead to frequent serious infections.
When to suspect an immune disorder?
One may suspect an immune disease in a child in the following situations:
- Repeated ear infections or sinus infections.
- More than 2 pneumonias in a year
- Recurrent, deep skin or organ abscesses
- Persistent thrush in mouth after one year of age
- A family history of primary immune deficiency.
- Unusual manifestation of a common infection
- Infection by an unusual organism
HIV is the commonest cause of acquired immune deficiency and basically leads to decrease in T lymphocytes (especially CD4 cells) leading to various infections and AIDS. However, there are several genetic defects (inborn defects) that can lead to dysfunction in B cells or T cells or both or neutrophils and can cause immune deficiency. These conditions are known as Primary Immunodeficiency Disease and over 70 primary immune deficiency disorders have been identified in last few decades.
The various primary immunodeficiency disorders seen are:
- Severe Combined Immunodeficiency (SCID): SCID is characterized by profoundly abnormal T cell function and antibody production. Patients usually present with chronic diarrhea, recurrent pneumonias and inability to put on weight. There are various types of SCID described, however the most common form is X-linked SCID seen in males. Children usually survive upto 1-2 years of age unless intervened. It is commonly called as “bubble boy disease”. Treatment consists of bone marrow transplant. Patients should avoid live viral vaccines and monthly injections of intravenous immunoglobulin (IVIG) may be required. IVIG are antibody injections
- Hyper IgM syndrome: Again this defect is more common in males and infants present with recurrent pneumonia, diarrhea and inability to gain weight. Here there is a defect in antibody conversion due to various genetic defects. Treatment again is bone marrow transplant and monthly injections of IVIG to decrease frequency of infections.
- Common Variable Immunodeficiency (CVID): Here, there is absent or ineffective antibody production. Patients present in 1st decade or 2nd decade of life with recurrent pneumonias. These patients require longer courses of antibiotics for their treatment. They have poor response to vaccines. Other associated features may be rheumatoid arthritis. The treatment consists of monthly IVIG therapy.
- IgA deficiency: This is the commonest type of primary immunodeficiency and occurs in 1 in 300 to 1 in 1,000 adults. It usually is diagnosed when screening family members of a patient with primary immunodeficiency. Most people with IgA deficiency are healthy. An exception to that are individuals who also lack IgG2, who are prone to severe bacterial infections. For patients with isolated IgA deficiency and no serious infections, no treatment is required. For patients with combined IgG2 deficiency, monthly IVIG is treatment of choice.
- Chronic mucocutaneous candidiasis: This is characterized by recurrent candidial (fungal) infection in mouth, fingernails, toe-nails and in females in the vagina. Patients may have associated thyroid problem or diabetes mellitus. Treatment consists of anti fungals.
- Hypogammaglobulinemia: This is characterized by low antibody production and recurrent bacterial infections. It is commonly seen after the age of 6 months and treatment consists of monthly IVIg.
Other primary immune deficiencies include Wiskott-Aldrich syndrome, defects in neutrophils and complement defects.
Conclusion: A child with recurrent and serious infections should be screened for an underlying immune defect be it an acquired (HIV) or an inborn defect (Primary Immunodeficiencies).
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