Immunodeficiency and its type

July 13, 2018

Introduction

Immunodeficiency diseases are condition where the defense mechanism of the body is impaired lading to repeated microbial infections of varying severity and sometimes enhanced susceptibility to malignancies.
In this condition, the system fails to protect the host from disease causing agents or from malignant cells.
Deficiency of defense mechanism may include:

Specific immune functions – humoral immunity, cell mediated immunity or both.
Nonspecific immune functions –phagocytes, complement system which augment and act in conjunction with specific immune response.

Immunodeficiency are mainly of two types . They are:

A) Primary immunodeficiency/ genetic deficiency/ congenital deficiency

B) Secondary immunodeficiency/ acquired immunodeficiency

A) Primary immunodeficiency

A condition resulting from a genetic or developmental defect of the immune system is called primary immunodeficiency.
Most of the primary immunodeficiency are inherited thus called genetic deficiencies or congenital deficiencies.
A primary immunodeficiency affects either adaptive or innate immune function.
In adaptive immunodeficiency T cell, B cell or both components are involved whereas in innate immunodeficiency, phagocytes or complement factors are involved.
Primary immunodeficiency can be categorized as:

a) Lymphoid immunodeficiency

b) Complement deficiency

c) Phagocytosis deficiency.

a) Lymphoid deficiency

It may involve T cells, B cells or both.
In B cells deficiency (Humoral deficiency), there appears complete absence of mature reticulating B cells, plasma cells and Ig.
This type of disorder have diverse spectrum of disease.
Patients with these disorders are usually subjected to recurrent bacterial infection but display normal immunity to most viral and fungal infections because the T cell branch of the immune system is largely unaffected.
e.g., X-linked agammaglobulinemia, transient hypo hammaglobulinemia of infancy, common variable immunodeficiency, selective immunoglobulin deficiency, Transcobalamin II deficiency.
In T cells (cellular deficiency), more severe and persistent infections are noticed than those of B cells defects.
Deficiency of T cells is associated with abnormal antibody level because T_Hcells are involved in the generation and control of antibody synthesis.
Abnormalities of T- lymphocyte development results in viral, intracellular bacterial, fungal and protozoan infection rather than acute bacterial infection.
e.g., Thymic hypoplasia (Di George syndrome), chronic muco-cutaneous candidosis, purine nucleoside phopshorylase (PNP) deficiency.
In combined immunodeficiency, both lineages are affected and are generally lethal.
The onset of infection begins early in infancy and the prognosis from these infant causes early death unless therapeutic intervention reconstitutes their defective number of option.
e.g.,Ataria telangiectasica, Wiskoh- Aldrich syndrome, Swis type agammaglobulinemia, etc.

b) Complement deficiency

It results from the defect of complement system.
It can be categorized as complement component deficiency and complement inhibitor deficiency.
Complement components deficiency have been detected in genetic deficiencies in human.
Genetic deficiencies of C10, C1γ, C1s, C4, and C2 component are associated with defects in activation of the classical pathway.
This result in increased susceptibility to pyogenic infection.
This may be transmitted as autosomal recessive traits.
Hereditary agioneurotic edema is due to the genetic deficiency of C1.
Deficiency of C3b in-activators has been associated with chronic recurrent pyogenic lesions.
This may be transmitted as autosomal dominant trait.
C3 deficiency results in defect of both classical and alternative pathways leading to pyogenic infection and in opsonization and phagocytosis.
Deficiency of properdin factor results in impaired activation of alternative pathway that results in pyogenic infection.

c) Phagocytic deficiency

It may be impaired by either intrinsic or extrinsic defects.
Intrinsic disorders may be due to defects within the phagocytic cells such as enzyme deficiency.
Extrinsic disorders may be due to deficiency of opsonin antibody, complement or other factors promoting phagocytosis or to the effects of drugs or anti-neutrophil auto-antibodies.
Phagocytic dysfunction leads to increased susceptibility to infection ranging from mild recurrent skin infections to overwhelming systemic infection.
e.g., chronic granulomatos disease, Job’s syndrome, etc.

B) Secondary immunodeficiency

It is the loss of immune function which arises when infection, drugs (like immunosuppressive agents, corticosteroids), nutritional in-adequencies, metabolic disorders and malignancies lead to defects in specific and non-specific immunity.
These are very common than primary immunodeficiency.
Deficiencies of humoral and cellular immune responses may occur secondarily during the course of many diseases process.
Various hormonal and metabolic disorders can also result in immune deficiency including anemia, hypothyroidism, diabetes and hypoglycemia.
Smoking, alcoholism and drug abuse also depress immune response.
The most well-known example of a secondary immune deficiency is the immunodeficiency caused by the human immunodeficiency virus, or HIV.
HIV attacks certain cells in the immune system and prevents them from carrying out their proper functions against microbes.
When the immune system is sufficiently weakened, infected people catch atypical and severe infections.
This is then called the Acquired Immunodeficiency Syndrome, or AIDS. AIDS at this time is often treated by a specialized multidisciplinary team.