Key Event Title
|Level of Biological Organization|
Key Event Components
|T cell activation involved in immune response||decreased|
Key Event Overview
AOPs Including This Key Event
|AOP Name||Role of event in AOP|
|Immune dysfunction induced by JAK3 inhibition||AdverseOutcome|
|Homo sapiens||Homo sapiens||High||NCBI|
|Mus musculus||Mus musculus||High||NCBI|
|All life stages||High|
Key Event Description
Antibody production to T-cell–dependent antigens is established through the coordination of B cells, antigen-presenting cells as well as T-cell–derived cytokines, which stimulate B cells to proliferate and differentiate. T-cell–dependent antibody response (TDAR) might be altered if any of these cell populations is affected.
IL-2 and IL-4 are produced and secreted by helper T cells and play important roles in the development of TDAR. IL-4 affects maturation and class switching of B cells as well as proliferation, both of which induces/enhances TDAR. IL-2 promotes differentiation of B cells through IL-2 stimulates differentiation of the activated T cell into Th2 cell. Therefore, suppressed production of IL-2 and IL-4 impairs TDAR (64-Justiz Vaillant-2020).
A mutant form of human IL-4, in which the tyrosine residue at position 124 is replaced by aspartic acid (hIL-4Y124D), specifically blocks IL-4 and IL-13-induced proliferation of B cells. In addition, hIL-4Y124D also strongly inhibited both IL-4 or IL-13-induced IgG4 and IgE synthesis in cultures of peripheral blood mononuclear cells, or highly purified sIgD + B cells cultured in the presence of anti-CD40 mAbs. It was suggested that IL-4 is necessary to product antibodies for B cells to proliferate B cells, and the mutation of IL-4 may cause the impairment of TDAR (65-Aversa-1993).
IL-4 stimulates B-cells to proliferate, to switch immunoglobulin classes, and to differentiate into plasma and memory cells. Suppressing the production of these B-cell–related cytokines appears to impair TDAR, as seen in the result of FK506 treatment (39-Heidt-2010).
STAT5 is able to inhibit PPAR (peroxisome proliferator activated receptors)-regulated gene transcription and conversely, ligand-activated PPAR able to inhibit STAT5-regulated transcription. As a peroxisome proliferator, PFOA is able to induce PPARs. The suppression of TDAR has been observed in a NOEL of 1.88 mg/kg/d and LOEL of 3.75 mg/kg/d identified for PFOA administered in drinking water over 15 days (66-Dewitt-2008). It was suggested that the increase of PPAR expression induced by PFOA inhibited STAT5-regulated transcription which is important for IL-4 production in TDAR.
How It Is Measured or Detected
TDAR could be examined in vivo and in vitro.
In vivo studies of antigen-specific antibodies are usually performed by measuring serum antibody levels with Enzyme-Linked ImmunoSorbent Assay (ELISA) (67-Onda-2014) or with a plaque-forming cell (PFC) assay.
To assess keyhole limpet hemocyanin (KLH) antigen-specific T cell proliferation, 1x105 CD4+ T cells were co-cultured with 2x105 autologous peripheral blood mononuclear cell (PBMCs) in 96-well plates in the presence of KLH. Cells were cultured for five or seven days before being pulsed with 0.5μCi 3[H]-thymidine (Perkin Elmer, Groningen; Netherlands) for 18 hours. The cells were harvested using a 96-well cell FilterMate harvester (PerkinElmer, Warrenville road IL, USA). 3[H]-thymidine incorporation was measured by liquid scintillation counting using a TopCount NXT (Perkin Elmer, Warrenville road CD4+ T cell response to biopharmaceuticals (68-Schultz-2017).
Rats were repeatedly administered FK506 orally for 4 weeks and immunized with KLH, after which the serum was examined for T-cell–dependent, antigen-specific, IgM and IgG levels using a Sandwich ELISA kit (69-Ulrich-2004).
Mice were repeatedly administered calcineurin inhibitors (CNIs) including FK506 and cyclosporin A (CsA) orally for 4 days and immunized with SRBC, after which spleen cells were examined using a PFC assay (70-Kino-1987). Antigen-specific plaque-forming splenocytes were reduced at dose levels of 3.2, 10, 32 and 100 mg/kg of FK506 or 32 and 100 mg/kg of CsA.
Cynomolgus monkeys received 50 mg/kg CsA twice a day via oral gavage (10 h apart) for 23 days and were immunized with SRBC, after which the serum was examined for Anti-SRBC IgM and IgG levels using an ELISA specific for SRBC antigen (71-Gaida-2015).
Mice were exposed a single pharyngeal aspiration of DBA, after which supernatants of splenocytes cultured for 24 h in the presence of LPS and assayed using a mouse IgM or IgG matched pairs antibody kit (Bethyl Laboratories, Montgomery, TX) (72-Smith-2010).
For in vitro studies, total IgM and IgG levels in culture supernatant are often measured after polyclonal T-cell activation rather than measuring antigen stimulation in immune cell cultures.
T cells and B cells isolated from human peripheral blood mononuclear cells (PBMC) were co-cultured with a CNIs for nine days in the presence of polyclonal–T-cell stimulation, after which supernatants were tested for immunoglobulin IgM and IgG levels using a Sandwich ELISA kit. Treatment with FK506 or CsA reduced the levels of IgM and IgG at the concentrations of 0.3 and 1.0 ng/mL (0.37 and 1.24 nM) or 50 and 100 ng/mL (41.6 and 83.2 nM) respectively (39-Heidt-2010).
SKW6.4 cells (IL-6-dependent IgM-secreting human B-cell line) were cultured with anti-CD3/CD28 antibody-stimulated PBMC culture supernatant. After culturing for four days, IgM produced in the culture supernatants was measured using an ELISA kit. FK506 or CsA reduced the levels of IgM at the concentrations of 0.01 to 100 ng/mL or 0.1 to 1000 ng/mL (73-Sakuma-2001).
Domain of Applicability
CNIs induced impairment of TDAR is demonstrated with rodent studies. That is, oral administration of FK506 or CsA to mice for 4 days impaired the response of PFC in splenocytes after intravenous immunization with sheep erythrocytes (70-Kino-1987). Likewise, oral administration of FK506 to rats over a four-week period reduced production of both anti-KLH-IgG and IgM antibodies after subcutaneous immunization with KLH (69-Ulrich-2004). Moreover, Treatment with CsA at 50 mg/kg BID via oral gavage in cynomolgus monkey resulted in reduction of serum SRBC-specific IgM and IgG (71-Gaida-2015). As for humans, in vitro experiments showed that treatment with FK506 or CsA of peripheral blood mononuclear cells from blood-bank donors suppressed the production of IgM and IgG antibodies specific to T-cell–dependent antigens (73-Sakuma-2001). Considering that FK506 and CsA reduce T cell-derived IL-2, these findings strongly suggest that impairment of TDAR following reduced production of IL-2 occurs at least in common among humans, monkey, and rodents.
Yang et al. (2002b) exposed male C57BL/6 mice to a single concentration (0.02%) of PFOA in the diet for 16 days. TDAR was measured after inoculating PFOA treated mice with horse red blood cells (HRBC) intravenously on day 10; serum levels of HRBC-specific IgM and IgG in response to the immunization were significantly decreased (74-Yang-2002).
The suppression of TDAR in adult C57BL/6J or C57BL/6N female mice has been observed in several studies and a NOEL of 1.88 mg/kg/d and LOEL of 3.75 mg/kg/d identified for PFOA administered in drinking water over 15 days (66-Dewitt-2008).
The suppression of TDAR in adrenalectomised (adx) or sham-operated C57BL/6N female mice has been observed for PFOA administration (0, 3.75, 7.5, or 15 mg/kg/d in drinking water for 10 days). Immune tests: TDAR, ie. primary antibody response to T-cell dependent antigen (SRBC). Day after exposure ended, i.v. SRBC with SRBC-specific IgM measurement 5d later (75-DeWitt-2009).
Evidence for Perturbation by Stressor
Regulatory Significance of the Adverse Outcome
Regulatory Significance of the Adverse Outcome
TDAR is considered to be the most important endpoint of immunotoxicity, because T cells, B cells, and antigen-presenting cells such as dendritic cells are involved in inducing and developing of TDAR. Thus, changes in any of these immune cell populations can influence TDAR.
Moreover, ICH S8 immunotoxicity testing guideline on pharmaceuticals recommends that TDAR can be evaluated whenever the target cells of immunotoxicity are not clear based on pharmacology and findings in standard toxicity studies. For the assessment for pesticides, US EPA OPPTS 870.7800 immunotoxicity testing guideline recommends TDAR using SRBC.
The draft FDA guidance of nonclinical safety evaluation for immunotoxicology recommends TDAR assay.
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