Suppression of IL-4 production leads to Impairment, TDAR

FK506 and rapamycin suppress the mRNA expression levels of IL-2 and IL-4 in T cells, which stimulate the proliferation of B cells (Heidt, et al. 2010).

Several in vivo studies in rodents have shown decreased TDAR following treatment with FK506 (Kino, et al. 1987, Ulrich, et al. 2004). In vitro tests examined antibody production in blood samples obtained from blood bank donors and PBMCs treated with FK506 and CsA. The suppressed production of immunoglobulin (Ig) M and G antibodies to T cell dependent antigens was demonstrated (Heidt, et al. 2010).

T cells, B cells, and antigen-presenting cells, such as dendritic cells, are involved in the induction and development of TDAR. Thus, changes in any of these immune cell populations can influence TDAR. However, concerning the suppression of humoral immunity induced by the inhibition of CN phosphatase activity, CNIs do not affect B cells directly. Rather, the effect is indirect via T cells. FK506 and CsA are capable of inhibiting immunoglobulin production when B cells are cultured with non-pre-activated T cells, but FK506 and CsA fail to inhibit immunoglobulin levels when pre-activated T cells are used to stimulate B cells. Hence, the inhibition of B-cell response by FK506 and CsA appears solely due to inhibition of T helper cells (Heidt, et al. 2010).

Therefore, it is concluded that decreased amounts of IL-4, in addition to IL-2, secreted from helper T cells, is the main factor in the suppression of TDAR.

Empirical support for the suppression of IL-4 production leads to impairment, and the T cell dependent antibody response is strong.

Rationale：

In CD3/PMA activated human T cells, FK506 suppressed the production of IL-2, IL-4, and IFN-γ at concentrations of 1.2 to 12.5 nM and inhibited the expression of IL-2, IL-4, and IFN-γ mRNA at concentrations of 10 nM (Dumont, et al. 1998).

After 9-day culture of B cells and non-pre-activated T cell stimulation with FK506 or CsA, the levels of IgM and IgG in the culture supernatant were reduced. The FK506 levels were 0.3 and 1.0 ng/mL (0.37 and 1.24 nM) and the CsA levels were 50 and 100 ng/mL (41 and 83 nM) (Heidt, et al. 2010).

After a 4-day culture of SKW6.4 IL-6-dependent IgM-secreting human B cells and anti-CD3/CD28 stimulation of the PBMC culture supernatant with FK506 or CsA, the level of IgM in the culture supernatant was reduced at concentrations of 0.01 to 100 ng/mL (0.01 to 124 nM) of FK506 and  0.1 to 1000 ng/mL (0.08 to 832 nM) of CsA (Sakuma, et al. 2001).

Rats were treated with FK506 for over 4 weeks and immunized with KLH. The serum concentrations of anti-KLH IgM and IgG were reduced at a dose of 3 mg/kg/day (Ulrich, et al. 2004).

In vitro suppression of T cell derived cytokines and T cell dependent antibody production or antibody production after polyclonal T cell stimulation showed similar dose responses to CNIs. Time gaps were found between these two KEs, which showed earlier onset of cytokine production and delayed onset of antibody production.

IL-2 affects multiple populations of immune cells expressing IL-2 receptors, while IL-4 mainly acts on B cells. Additional suppression of other immune functions may also be possible.

In a rat T cell proliferation assay, IL-2-induced T cell proliferation was inhibited by peficitinib in a concentration-dependent manner with an IC50 of 10 nM and by tofacitinib with a similar IC50 of 24 nM (Gianti and Zauhar 2015). In addition, cynomolgus monkeys treated with CsA showed suppression of IL-2 and TDAR using SRBCs in a dose-dependent manner (Gaida, et al. 2015).\

In the human T-B-cell co-culture stimulated with anti-CD3 monoclonal antibody, CNIs of FK506 and CsA lowered the mRNA levels of T cell cytokines at 8 h post-stimulation including IL-2 and IL-4 at 1.0 ng/mL (1.24 nM) FK506 or 100 ng/mL (90.7 nM) CsA, and inhibited IgM and IgG productions after 9 days at 0.3 and 1.0 ng/mL FK506 and 50 and 100 ng/mL CsA (Heidt, et al. 2010).

In human T cell culture, suplatast tosilate (an inhibitor of the production of cytokines by Th2 cells) inhibited IL-4 production after 3 days and antigen-specific IgE production after 10 days (Taiho 2013).

Other authors described that in human T-B-cell co-cultures, FK506 and CsA lowered the mRNA levels of IL-2 and IL-4 at 8 h post-stimulation and inhibited IgM and IgG production after 9 days (Heidt, et al. 2010).

Treatment with CsA (50 mg/kg) twice daily in cynomolgus monkeys resulted in reduction of IL-4 cytokine production from PMA/ionocycin stimulation of whole blood starting on day 0 and continuing through the end of the study on day 16. CsA treatment achieved 82 [±10]%, 68 [± 25]%, and 82 [± 9]% 100% maximal inhibition of ex vivo IL-4 response on days 0, 9, and 16. SRBC-specific IgM and IgG were significantly lower in animals dosed with CsA than in animals dosed with the vehicle control on days 9, 12, and 16 post-immunization. There was ≥80% or greater reduction in SRBC-specific IgM on days 9–16. SRBC-specific IgG was decreased by ≥95% on days 9–16 (Gaida, et al. 2015). This was similar to the degree of inhibition observed in rats using an KLH immunization model (Smith, et al. 2003).

B cells are required for the generation and / or maintenance of Th2 responses. Germinal center B cells regulate Th2 development through an IL-4 dependent process. Type 2 immunity and allergic responses are initiated by T cells and DCs, this response may be sustained and potentially amplified by an IL-4-driven feedback loop between Ag-specific T and B cells (Harris, et al. 2005).