Immunoglobulin Deficiency Syndromes (more)

[Guest guest]

Immunoglobulin Deficiency Syndromes

L. Longe

Definition

Immunoglobulin deficiency syndromes are a group of immunodeficiency

disorders in which the patient has a reduced number of or lack of

antibodies.

Description

Immunoglobulins (Ig) are antibodies. There are five major classes of

antibodies: IgG, IgM, IgA, IgD, and IgE.

IgG is the most abundant of the classes of immunoglobulins. It is the

antibody for viruses, bacteria, and antitoxins. It is found in most

tissues and plasma.

IgM is the first antibody present in an immune response.

IgA is an early antibody for bacteria and viruses. It is found in

saliva, tears, and all other mucous secretions.

IgD activity is not well understood.

IgE is present in the respiratory secretions. It is an antibody for

parasitic diseases, Hodgkin's disease, hay fever, atopic dermatitis,

and allergic asthma).

All antibodies are made by B-lymphocytes (B-cells). Any disease that

harms the development or function of B-cells will cause a decrease in

the amount of antibodies produced. Since antibodies are essential in

fighting infectious diseases, people with immunoglobulin deficiency

syndromes become ill more often. However, the cellular immune system

is still functional, so these patients are more prone to infection

caused by organisms usually controlled by antibodies. Most of these

invading germs (microbes) make capsules, a mechanism used to confuse

the immune system. In a healthy body, antibodies can bind to the

capsule and overcome the bacteria's defenses. The bacteria that make

capsules include the streptococci, meningococci, and Haemophilus

influenzae. These organisms cause such diseases as otitis, sinusitis,

pneumonia, meningitis, osteomyelitis, septic arthritis, and sepsis.

Patients with immunoglobulin deficiencies are also prone to some

viral infections, including echovirus, enterovirus, and hepatitis B.

They may also have a bad reaction to the attenuated version of the

polio virus vaccine.

There are two types of immunodeficiency diseases: primary and

secondary. Secondary disorders occur in normally healthy bodies that

are suffering from an underlying disease. Once the disease is

treated, the immunodeficiency is reversed. Immunoglobulin deficiency

syndromes are primary immunodeficiency diseases, occurring because of

defective B-cells or antibodies. They account for 50% of all primary

immunodeficiencies, and they are, therefore, the most prevalent type

of immunodeficiency disorders.

X-linked agammaglobulinemia is an inherited disease. The defect is on

the X chromosome and, consequently, this disease is seen more

frequently in males than females. The defect results in a failure of

B-cells to mature. Mature B-cells are capable of making antibodies

and developing " memory, " a feature in which the B-cell will rapidly

recognize and respond to an infectious agent the next time it is

encountered. All classes of antibodies are decreased in

agammaglobulinemia.

Selective IgA deficiency is an inherited disease, resulting from a

failure of B-cells to switch from making IgM, the early antibody, to

IgA. Although the B-cell numbers are normal, and the B-cells are

otherwise normal (they can still make all other classes of

antibodies), the amount of IgA produced is limited. This results in

more infections of mucosal surfaces, such as the nose, throat, lungs,

and intestines.

Transient hypogammaglobulinemia of infancy is a temporary disease of

unknown cause. It is believed to be caused by a defect in the

development of T-helper cells (cells that recognize foreign antigens

and activate T- and B-cells in an immune response). As the child

ages, the number and condition of T-helper cells improves and this

situation corrects itself. Hypogammaglobulinemia is characterized by

low levels of gammaglobulin (antibodies) in the blood. During the

disease period, patients have decreased levels of IgG and IgA

antibodies. In lab tests, the antibodies that are present do not

react well with infectious bacteria.

Common variable immunodeficiency is a defect in both B cells and T-

lymphocytes. It results in a near complete lack of antibodies in the

blood.

Ig heavy chain deletions is a genetic disease in which part of the

antibody molecule isn't produced. It results in the loss of several

antibody classes and subclasses, including most IgG antibodies and

all IgA and IgE antibodies. The disease occurs because part of the

gene for the heavy chain has been lost.

Selective IgG subclass deficiencies is a group of genetic diseases in

which some of the subclasses of IgG are not made. There are four

subclasses in the IgG class of antibodies. As the B-cell matures, it

can switch from one subclass to another. In these diseases there is a

defect in the maturation of the B-cells that results in a lack of

switching.

IgG deficiency with hyper-IgM is a disease that results when the B-

cell fails to switch from making IgM to IgG. This produces an

increase in the amount of IgM antibodies present and a decrease in

the amount of IgG antibodies. This disease is the result of a genetic

mutation.

Causes and symptoms

Immunoglobulin deficiencies are the result of congenital defects

affecting the development and function of B lymphocytes (B-cells).

There are two main points in the development of B-cells when defects

can occur. First, B-cells can fail to develop into antibody-producing

cells. X-linked agammaglobulinemia is an example of this disease.

Secondly, B-cells can fail to make a particular type of antibody or

fail to switch classes during maturation. Initially, when B-cells

start making antibodies for the first time, they make IgM. As they

mature and develop memory, they switch to one of the other four

classes of antibodies. Failures in switching or failure to make a

subclass of antibody leads to immunoglobulin deficiency diseases.

Another mechanism that results in decreased antibody production is a

defect in T-helper cells. Generally, defects in T-helper cells are

listed as severe combined immunodeficiencies.

Symptoms are persistent and frequent infections, diarrhea, failure to

thrive, and malabsorption (of nutrients).

Diagnosis

An immunodeficiency disease is suspected when children become ill

frequently, especially from the same organisms. The profile of

organisms that cause infection in patients with immunoglobulin

deficiency syndrome is unique and is preliminary evidence for this

disease. Laboratory tests are performed to verify the diagnosis.

Antibodies can be found in the blood. Blood is collected and analyzed

for the content and types of antibodies present. Depending on the

type of immunoglobulin deficiency the laboratory tests will show a

decrease or absence of antibodies or specific antibody subclasses.

Treatment

Immunodeficiency diseases cannot be cured. Patients are treated with

antibiotics and immune serum. Immune serum is a source of antibodies.

Antibiotics are useful for fighting bacteria infections. There are

some drugs that are effective against fungi, but very few drugs that

are effective against viral diseases.

Bone marrow transplantation can, in most cases, completely correct

the immunodefiency.

Prognosis

Patients with immunoglobulin defiency syndromes must practice

impeccable health maintenance and care, paying particular attention

to optimal dental care, in order to stay in good health.