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Medical Microbiology, PAMB 650/720 - Fall 2009
M. Nagarkatti

Lecture 22-23

1. Understand Primary and Secondary immunodeficiencies
2. Characterization, diagnosis and treatment of various immunodeficiencies
3. Studies on HIV and Development of AIDS
4. Analysis of Strategies for Prevention and Treatment of AIDS

Immunodeficiency is the failure ofthe immune system to protect against disease or malignancy.
Primary Immunodeficiency is caused by genetic or developmental defect in the immune system. These
defects are present at birth but may show up later on in life.
Secondary or Acquired Immunodeficiency is the loss of immune function as a result of exposure to disease
agents, environmental factors, immunosuppression, or aging.

Typesof Primary Immunodeficiency Disorders
Defect in the hematopoietic stem cells results in reticular dysgenesis that leads to generalized immune defects
and subsequent susceptibility to infections. This condition is fatal if left untreated, but can be successfully treated
with bone marrow transplantation.

Myeloid Lineage deficiency: This deficiency involves myeloid progenitor cells and affectsinnate

Inasmuch as, phagocytosis is affected, the patients are susceptible to bacterial infections.

Congenital Agranulomatosis:
Patients have a decrease in the neutrophil count. It is due to a defect in the myeloid progenitor cell differentiation
into neutrophils. These patients are treated with granulocyte-macrophage colony stimulating factor (GM-CSF) or
ChronicGranulomatous Disease (CGD):
This is characterized by defective reactive oxygen species (ROS) production which normally kills phagocytosed
bacteria. However, they exhibit inflammatory reaction with neutrophils, macrophages and T cells resulting in the
formation of granulomas. The disease is detected by a negative reaction in the nitroblue tetrazolium test which in
normal individual turns blue due toreduction by superoxide anions. This is an autosomal recessive or X-linked
trait. Treatment is with interferon-γ (IFN-γ).
Leukocyte adhesion Deficiency (LAD):
Lack of CD18 (β chain) on T cells and macrophages impairs adhesion of these cells to endothelium thereby
preventing inflammation. Treatment is with bone marrow (devoid of T cells and MHC-matched) transplantation
or gene therapy.Lymphoid lineage immunodeficiency:
If the lymphoid progenitor cells are defective, then both the T and B cell lineages are affected and result in the
severe combined immunodeficiency (SCID). They are less common but are very severe. Such infants suffer
from recurrent infections especially by opportunistic microorganisms. These include the following disorders.
Patients having both T and B celldeficiency lack recombinase activating genes (RAG1 and 2) that are
responsible for the T cell receptor and Ig gene rearrangements. These patients are athymic and are diagnosed by
examining the T cell receptor (TCR) gene rearrangement. They also lack B cells although they do have Abs in



early infant life because of passive transfer from mother. NK cells are normal in these patients.This is an
autosomal recessive trait.
Interleukin-2 Receptor (IL-2R) may be lacking in patients thereby preventing signaling by IL-2 and other
cytokines which act as growth factors. This would lead to defect in the proliferation of T cells, B cells and NK
cells. This is an autosomal recessive trait.
Adenosine deaminase (ADA) is an enzyme responsible for converting adenosine to inosine. ADAdeficiency
leads to accumulation of adenosine which results in production of toxic metabolites that interfere with DNA
synthesis. The patients have defects in T, B and NK cells.
These SCID are autosomal recessive traits. Treatment is by gene therapy or stem cell transplantation.

T cell deficiency affects both cell-mediated and humoral immunity. The patients are susceptible to viral,
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