Section 2 Flow Cytometry

**27**

**Chapter 2**

**Abstract**

primary immunodeficiencies.

**1. Introduction**

Flow Cytometry Applied to

*Mónica Martínez-Gallo and Marina García-Prat*

**Keywords:** primary immunodeficiencies, lymphocyte subsets, extended immunophenotyping, flow cytometry, functional assays, intracellular cytokine production, cytotoxicity, phospho-stat flow

Primary immunodeficiencies are the result of biological defects associated with functional immune abnormalities. It consists of a group of disorders showing a higher incidence and severity of infections, expression of immunological dysregulation such as inflammation and lymphoproliferation. The immunophenotyping and *in vitro* functional characterization of immunodeficient patients contribute, together with the clinical aspects, to define the underlying immune defect particularities. Flow cytometry applications in primary immunodeficiency assessment are multiple and include the study of a wide range of specific cell lymphocyte subpopulations. This chapter describes the main techniques used in the diagnosis of a wide variety of primary immunodeficiencies, in which intracellular proteins or activation markers involved in immunity are evaluated, as well as functional proliferation, cytokine production, phosphorylation of transcription factors, cytotoxic and degranulation capacity. Flow cytometry is a tool that allows rapid and accurate evaluation of multiple lymphocyte populations and immunological function, and this information is essential for the diagnosis and evaluation of patients with

Primary immunodeficiencies (PID) are a heterogeneous group of genetic disorders which manifest clinically as recurrent infections, autoimmune and/or autoinflammatory diseases or malignancies. In PIDs, the immune system is affected quantitatively or qualitatively and includes more than 400 different entities, with an incidence of approximately 1:2000 live newborns. The Expert Committee of the International Union of Immunological Societies has classified PIDs into nine groups based on the clinical manifestations and laboratory immunological abnormalities [1]. Prompt identification of PID patients reduces complications and is associated with a more favorable prognosis [2]. In addition to a complete medical history, physical examination, and general laboratory tests, the initial evaluation protocol when PID is suspected includes analysis of serum immunoglobulin levels and extended immunophenotyping in peripheral blood. Immunophenotype abnormalities can range from a complete absence of a specific cell population to

the Diagnosis of Primary

Immunodeficiencies
