immune disorders

Immunological Disorders

Immunodeficiency

Overview of Immunodeficiency Disorders

  • Immunodeficiencies: Defined as a lack of sufficient immune response.

  • Two main categories of immunodeficiencies:

    • Primary (congenital): Results from genetic defects or environmental factors that impair the development of the immune system.

    • Secondary (acquired): Occur due to infections or other stresses on the immune system, such as malnutrition.

Primary Immunodeficiencies

  • Rareness: Primary immunodeficiencies are generally rare within the population.

  • Impact on Immune Cells: These disorders may involve defects affecting:

    • B cells

    • T cells

    • Natural killer (NK) cells

    • Phagocytes

    • Complement components

  • Known Gene Defects: There are numerous identified genetic defects that cause these deficiencies.

Types of Primary Immunodeficiencies

  1. Antibody Deficiencies:

    • Selective IgA deficiency: Characterized by little or no production of IgA antibodies.

    • Agammaglobulinemia: Condition where there are few or no antibodies produced.

  2. Lymphocyte Deficiencies:

    • Severe Combined Immunodeficiency (SCID): Occurs when hematopoietic stem cells in bone marrow do not produce T and B lymphocytes.

    • DiGeorge Syndrome: A condition where the thymus does not develop in the embryo, leading to an absence of differentiated T cells.

Defects in Phagocytic Cells

  • Various conditions affect the function and efficacy of phagocytic cells:

    • Chronic Granulomatous Disease (CGD): Characterized by the inability to produce hydrogen peroxide and other reactive oxygen species, hampering phagocytes' ability to kill certain pathogens.

    • Chediak-Higashi Disease: Results from lysosomes lacking certain enzymes, rendering them unable to destroy phagocytized bacteria.

    • Leukocyte Adhesion Deficiency: A condition where white blood cells cannot leave circulation to concentrate at areas of infection.

Defects in Complement System Components

  • Deficiencies in complement system components lead to various issues:

    • Lack of early components (C1, C2) may result in immune complex diseases.

    • Absence of late components (C5, C6, C7, C8) can lead to recurring infections by Neisseria due to a lack of Membrane Attack Complexes (MACs).

    • A deficiency in C1-inhibitor leads to uncontrolled complement activation.

Secondary Immunodeficiencies

  • Causes: Secondary immunodeficiencies arise from multiple factors including:

    • Malignancies

    • Advanced age

    • Pregnancy

    • Infections (with a focus on viral causes)

    • Immunosuppressive drugs

    • Malnutrition

Impact of Viral Infections on Immunity

  • Specific viral infections can lead to depletion of critical immune cells:

    • Measles: Replicates within lymphoid cells and destroys them, significantly impairing the immune response.

    • Syphilis, leprosy, malaria: Impact the T-cell population and compromise macrophage function.

    • HIV: Destroys helper T cells, leading to Acquired Immunodeficiency Syndrome (AIDS).

Case Study: Multiple Myeloma

  • Description: Multiple myeloma is a malignancy originating from a single plasma cell that proliferates uncontrollably.

  • Effect on Immunoglobulin Production: Produces excessive amounts of one type of immunoglobulin while depleting other necessary immunoglobulins needed for effective immune responses against infections.