The human immune system is a complex defence system, consisting of cells and proteins
that act together; to fight infections caused by bacteria, viruses, and parasites.
We are constantly exposed to infectious agents, and everyone gets
an infection once in a while. However, some people get recurrent infections. There
are several reasons for these individuals to have an increased susceptibility
In assessing the child with recurrent infections one need's to remember the rarity
of true immunodefeciency and the high prevalence of allergy (atopy), exposure to
cigarette smoke, attendance to day care (with high level exposure to bugs), and
anatomic variations as predisposing factors for infections.
The Immune System
The major function of the immune system is to recognise foreign
substances and react to them. An immune system that is functioning
adequately should defend the body from infectious organisms (bacteria, viruses,
fungi, and parasites) and protect the body from development of cancers. The major
organs of the immune system include the bone marrow, liver, thymus, tonsils, lymph
nodes, the spleen, and blood. These organs manufacture, process and store the major
components of the immune system, which include:
T- Lymphocytes or T-cells – White blood cells important in
regulating the immune system and helping fighting viral infections.
B- Lymphocytes or B-cells – Cells that make specific proteins
called antibodies to protect from bacteria that cause ear infections,
sinusitis and pneumonia, etc. The chemical name for antibody proteins is immunoglobulins
or gammaglobulins. There are four major classes of antibodies or immunoglobulins:
- Immunoglobulin G (IgG)
- Immunoglobulin A (IgA)
- Immunoglobulin M (IgM)
- Immunoglobulin E (IgE)
Each immunoglobulin class has special chemical characteristics that provide it with
specific advantages. For example, antibodies in the IgG fraction are formed in large
quantities, last for over a month and travel from the blood stream to the tissues
easily. The IgG antibodies are the only immunoglobulins that cross the placenta
and pass immunity from the mother to the newborn. Because our immune system can't
make the most important antibody, IgG, in sufficient quantity until about six months
of age, IgG antibodies passed on by a mother before birth, protects the baby. If
the baby's own immune system does not "turn on" at the right time, the child may
get recurrent infections. This is called "Transient hypogammaglobulinemia
(low immunoglobulin) of infancy", transient because the child will outgrow it by
the age of 2 or 3 years, as the immune system matures.
IgA antibodies are produced near mucous membranes and find their way into secretions
such as tears, saliva, and mucus, where they protect against infection in the respiratory
tract and intestines.
IgM antibodies are the first antibodies to be formed in response to infection. Therefore,
they are important in the early days of an infection.
IgE antibodies are responsible for allergic reactions and parasitic infections.
Phagocytes – Cells that ingest foreign bodies and bacteria
to kill them.
Complement – Proteins that may kill bacteria that may cause
A Primary Immunodeficiency occurs when the abnormality to the immune
system develops from an inborn defect in the cells. It is a disorder in immune function
that is not a result of infection (eg. AIDS) or extrinsic manipulation. The cells
that are affected include T-cells, B-cells, phagocytic cells, or the complement
system. Most primary immune deficiencies are inherited diseases.
is not always evident at birth
. There are about 95 known primary immunedeficiency
diseases. Some examples of Primary Immunodeficiencies include:
Selective IgA deficiency – relatively common, about 1/333 – 1/1000 in
- Severe common immunodefeciency (SCID)
- Common variable immunodefeciency (CVID)
- X-linked Agammaglobulinemia (XLA)
While primary immune deficiencies are uncommon it is essential they be diagnosed
promptly to prevent damage to organs such as the lungs and ears, and also to prevent
life threatening infections. A careful history, physical examination, and sometimes
a simple blood test are often all that is required to rule out an underlying immune
Secondary Immune deficiencies occur when damage is caused by an
environmental factor. Radiation, chemotherapy, burns, and infections contribute
to the many causes of secondary immune deficiencies. Acquired Immune Deficiency
is a secondary immune deficiency caused by the Human Immunedeficiency Virus (HIV).
In Leukemia, Lymphomas, and metastatic cancer, abnormal cancerous cells crowd out
normal stem cells of the bone marrow. These abnormal cells reduce the number of
B cells and lead to hypogammaglobulinemia or secondary immune deficiency.
10 Warning signs of Primary Immunodeficiency
(Compiled by the Medical Advisory Board of Jeffery Modell Foundation)
- 8 or more ear infections within 1 year
- 2 or more serious sinus infections within 1 year
- 2 or more months on antibiotics with little effect
- 2 or more pneumonia within 1 year
- Failure of an infant to gain weight or grow normally
- Frequent deep skin or organ abscesses
- Need for intravenous antibiotics to clear infections
- Persistent thrush in the mouth or elsewhere on the skin after 12 months of age
2 or more deep seeded infections such as meningitis, osteomyelitis, cellulitis,
- Family history of Primary Immunodeficiency
Common Infections caused by increased exposure to bugs seen in normal
A study in the USA in the 80's showed that recurring middle-ear infections among
preschoolers rose sharply between 1981 and 1988, in part because more children were
in day care centres than before.
The most common infections are viral respiratory tract infections (the common cold).
The average young child may get up to 12 colds a year. Typically, cold symptoms
last 5-10 days. These frequent colds are usually not a cause for concern, as colds
are a result of the close contact of young children with a relatively immature immune
Allergies and recurrent infections
In people with allergies, there is an over-reaction and loss of control, where the
immune system launches attack against a perfectly harmless substance, such as grass
pollen, cat dander or peanut or penicillin. The harmful end results of these attacks
are called immediate hypersensitivity or allergy.
The first line of defence against infection is located where the body has contact
with the rest of the world. In atopic eczema, where the skin barrier is often broken
from scratching, it is easy for organisms to enter the skin and cause infection.
Similarly, inflammation (irritation, swelling and injury) to the mucous membranes
lining the nose, sinuses, and lungs provide a fertile ground for secondary infections.
In patients who have year-round allergies to house dust mites, pollen and moulds,
there will be some injury to the mucus membranes, which increases their susceptibility
Nasal blockage due to allergic rhinitis is also thought to lead to secretions and
eustachian tube blockages that promote ear infections.
Many people confuse persistent (perennial) allergic rhinitis due to house dust mites
or cat allergy with a prolonged cold or sinus infection, since the symptoms of nasal
stuffiness, nasal itch, and runny nose are common to both. It is therefore important
for all patients with "prolonged cold symptoms or sinusitis" to have a skin prick
test for inhalant allergens.
There is also good evidence to suggest that atopic (allergic) individuals have an
inherited defective (abnormal) B and T cell functioning, which contributes to their
increased risk (and prolongation) of infections.
Structural (Anatomical) changes causing recurrent Infections
Structural changes in the sinuses or Eustachian tubes (connecting tubes in each
ear) are a cause of repeated infections in childhood. The term "structural changes"
refers to differences in the bony parts of the skull, the sinuses, and ears. These
differences are often inherited. These differences in body structure makes it easier
for that person to get infections because the normal drainage of the (Eustachian
tubes (in the ear) or sinuses (in the nose) is blocked. Another common anatomical
variation (abnormality) is a deviated nasal septum (the cartilage, usually midline,
which separates right and left nostrils. This predisposes to improper drainage of
the sinuses on the narrower side, especially when there is also nasal blockage from
any cause, but commonly from allergic rhinitis.
Recurrent infections in early childhood are usually normal, and relate to a relatively
immature immune system.
Allergies can present as recurrent infections, or be a predisposing factor for recurrent
infections, therefore all kids with recurrent infections should be considered for
skin prick testing.
Primary Immunodeficiency is rare but should be considered in anyone with recurrent
infections, especially if the infections are severe, difficult to treat or caused
by unusual bugs.
While primary immune deficiencies are uncommon it is essential they be diagnosed
promptly to prevent organ damage and life-threatening infections.
A careful history, physical examination, and sometimes a simple blood test are often
all that is required to rule out an underlying immune deficiency.
I thank Dr Jan P. Sinclair, Allergist and Paediatrician, for her contribution to