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Related Concept Videos

Immunodeficiency Diseases01:25

Immunodeficiency Diseases

Immunodeficiency disorders are conditions in which the immune system's ability to fight infectious disease and cancer is compromised or entirely absent. The immune system comprises a complex network of cells, tissues, and organs that work together to protect the body from potentially harmful invaders. When this system is deficient or not functioning properly, it leaves the body susceptible to infections, diseases, or other complications.
There are three main causes of immunodeficiency disorders...
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Humoral Immune Responses

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Development of Immunocompetence01:22

Development of Immunocompetence

The initiation of cell-mediated immunity can be observed as early as the third month of fetal growth, with active antibody-mediated immunity following approximately one month later.
The initial cells that migrate from the fetal thymus settle within the skin and epithelial tissues lining the mouth, digestive tract, and in females, the uterus and vagina. These cells, including skin-based dendritic cells, serve as antigen-presenting cells, playing a key role in T cell activation.
Subsequent T...
Special Features of Adaptive Immunity01:20

Special Features of Adaptive Immunity

The adaptive immune system, a crucial component of the overall immune response, offers a highly specialized defense against pathogens. It involves specific cell types and features, enabling it to combat infections effectively and efficiently.
The primary cell types involved in adaptive immunity are T cells and B cells. Each type has a unique role in defending the body against pathogens. T cells are responsible for cell-mediated immunity. They identify and eliminate infected cells directly,...
Immunological Memory01:23

Immunological Memory

Immunological memory, a pivotal pillar of the adaptive immune system, is responsible for the body's ability to remember and respond more swiftly and effectively to previously encountered pathogens. This remarkable feature is what makes vaccines so effective in preventing diseases.
What is Immunological Memory?
Immunological memory is an integral function of the immune system that allows it to recognize and react more rapidly and effectively to pathogens previously encountered. This feature is...
B Cell Activation and Differentiation01:24

B Cell Activation and Differentiation

The adaptive immune response, a sophisticated defense mechanism, relies on the activation and differentiation of B lymphocytes, or B cells. These processes enable our bodies to mount a tailored response against specific pathogens such as bacteria, free virus particles, toxins, and parasites.
When naive B cells encounter a specific antigen that can bind to the B cell receptor (BCR) on their surface, they undergo sensitization to respond to the antigen's presence. Sensitization begins with...

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Related Experiment Video

Updated: May 21, 2026

Simultaneous Quantification of T-Cell Receptor Excision Circles (TRECs) and K-Deleting Recombination Excision Circles (KRECs) by Real-time PCR
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Simultaneous Quantification of T-Cell Receptor Excision Circles (TRECs) and K-Deleting Recombination Excision Circles (KRECs) by Real-time PCR

Published on: December 6, 2014

Defining combined immunodeficiency.

Chaim M Roifman1, Raz Somech, Fotini Kavadas

  • 1Division of Immunology and Allergy, Hospital for Sick Children and University of Toronto, Toronto, Ontario, Canada. chaim.roifman@sickkids.ca

The Journal of Allergy and Clinical Immunology
|June 6, 2012
PubMed
Summary
This summary is machine-generated.

Severe combined immunodeficiency (SCID) is defined by fewer than 500 circulating T cells. Some T-cell deficiencies (TD) with autologous T cells may not be detected by newborn screening using T-cell receptor excision circle (TREC) analysis.

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Area of Science:

  • Immunology
  • Genetics
  • Pediatrics

Background:

  • Severe combined immunodeficiency (SCID) is a profound T-cell dysfunction (TD).
  • Less typical T-cell deficiencies present with autologous circulating T-cell combined immunodeficiency (CID).
  • Distinguishing CID from SCID is crucial for bone marrow transplantation protocols.

Purpose of the Study:

  • Determine circulating T-cell counts in SCID versus CID patients.
  • Assess T-cell function in these patient groups.
  • Evaluate the utility of T-cell receptor excision circle (TREC) analysis for newborn screening.

Main Methods:

  • Flow cytometry to quantify CD3(+) T cells.
  • In vitro T-cell response assays (e.g., PHA stimulation).
  • TREC level analysis in patient samples.

Main Results:

  • Typical SCID patients had <500 CD3(+) T cells/μL with reduced PHA response.
  • Patients with CID showed variable T-cell counts and responses.
  • TREC levels were low in typical SCID, Omenn syndrome, and ZAP70 deficiency.
  • Normal TREC levels were observed in some TD patients (e.g., FOXP3, CD40L, IL10RA deficiencies).

Conclusions:

  • Fewer than 500 circulating CD3(+) T cells define typical SCID.
  • Many patients with autologous T cells still exhibit profound TD.
  • TREC-based newborn screening may miss some TD cases with normal TREC levels.