MONITORING THE CELLULAR COMPONENTS OF THE IMMUNE SYSTEM DURING CLINICAL TRIALS: A TRANSLATIONAL MEDICINE APPROACH - Flow Cytometry in Drug Discovery and Development - page 190

T-helper lineage, has been described. Th17 differentiation is induced by TGF- b , IL-6,
and maintained IL-23 [10]. Th17 cells secrete IL-17 (a potent proinflammatory
cytokine), IL-21, and IL22 and are potent inducers of tissue inflammation and the
clearance of pathogens not adequately controlled by Th1 and Th2 cells [11]. They
play a key role in driving autoimmune pathologies [12]. Treg cells are identified
phenotypically as CD4 þ , CD25bright, and intracellular Foxp3 þ , and prevent
immune attack against normal and neoplastic cells by directly suppressing the
activation of effector CD4 þ and CD8 þ T cells [13].
Antigen activation of na ve B cells (CD19 þ , sIgM þ , sIgD þ ) results in generation

of memory B cells (CD19 þ , CD27 þ , sIgD ) and terminally differentiated plasma
cells that secrete large quantities of antigen-specific antibody (Ab).

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9.3 CLINICAL RESEARCH: CHARACTERIZATION OF
ABNORMALITIES OF THE CELLULAR COMPONENTS
OF THE IMMUNE SYSTEM

Many diseases and syndromes fall under the umbrella of inflammatory autoimmune
disorders such as systemic lupus erythematosus (SLE), rheumatoid arthritis (RA),
psoriasis, Crohn's disease, Sjogren's syndrome, and systemic sclerosis. Most of these
rheumatic disorders are heterogeneous diseases with a clinical spectrum, ranging
from mild to life threatening, and variability in secondary organ system involvement
(e.g., kidney and heart). Clinical research scientists are actively studying patients with
autoimmune disorders with the goal of elaborating the pathophysiology and identify-
ing disease-specific molecular signatures. There is a growing body of literature
suggesting that hyper-responsive B cells, abnormalities in T-lymphocyte cell signal-
ing, and abnormalities in Treg function contribute to the development of autoimmune
inflammation. Nevertheless, the cause of these disorders and their pathogenesis
remains poorly understood [14-16]. To illustrate the importance and utility of the
research conducted by clinical scientists, three examples will be focused on.
SLE is primarily a disease of B-cell origin characterized by the loss of immune
tolerance to multiple self-antigens resulting in the production of numerous auto-
antibodies, in particular, antinuclear autoantibodies [14, 17]. There is a correlation
between SLE flare-ups and systemic B-cell activation, defined as an expansion of
plasma blasts/plasma cells (CD19 þ , CD20 ) and pregerminal center cells (CD19 þ ,
IgD þ , CD38high) combinedwith a decrease in circulating na ve B cells. In particular,

an increase in a homogeneous subset of CD27 , IgD , and CD95 þ memory B cells
shows a strong correlationwith disease activity [18]. Thus, chronic B-cell activation is
gaining acceptance as a pathogenic biomarker for SLE [19].
Several T-cell abnormalities have also been characterized in SLE patients.
Spontaneous apoptosis of circulating T cells is thought to contribute to chronic
lymphopenia and the generation of autoantigens [20]. Double-negative (DN) T cells
(CD3 þ , CD4 , and CD8 ) are also thought to contribute to SLE pathogenesis as they
are expanded in the peripheral blood of SLE patients and have been shown to be potent
producers of the inflammatory cytokines IL-17 and IFN- g [21]. Likewise, extensive

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