ICOS-Expressing CD4 T Cells Induced via TLR4 in the Nasal Mucosa Are Capable of Inhibiting Experimental Allergic Asthma

Abstract

Modulation of adaptive immune responses via the innate immune pattern recognition receptors, such as the TLRs, is an emerging strategy for vaccine development. We investigated whether nasal rather than intrapulmonary application of Protollin, a mucosal adjuvant composed of TLR2 and TLR4 ligands, is sufficient to elicit protection against murine allergic lower airway disease. Wild-type, Tlr2−/−, or Tlr4−/− BALB/c mice were sensitized to a birch pollen allergen extract (BPEx), then received either intranasal or intrapulmonary administrations of Protollin or Protollin admixed with BPEx, followed by consecutive daily BPEx challenges. Nasal application of Protollin or Protollin admixed with BPEx was sufficient to inhibit allergic lower airway disease with minimal collateral lung inflammation. Inhibition was dependent on TLR4 and was associated with the induction of ICOS in cells of the nasal mucosa and on both CD4+Foxp3+ and CD4+Foxp3− T cells of the draining lymph nodes (LNs), as well as their recruitment to the lungs. Adoptive transfer of cervical LN CD4+ICOS+, but not CD4+ICOS−, cells inhibited BPEx-induced airway hyperresponsiveness and bronchoalveolar lavage eosinophilia. Thus, our data indicate that expansion of resident ICOS-expressing CD4+ T cells of the cervical LNs by nasal mucosal TLR4 stimulation may inhibit the development of allergic lower airway disease in mice.

Modulation of Distinct Asthmatic Phenotypes in Mice by Dose-Dependent Inhalation of Microbial Products

“…For example, Foxp3 + CD4 + nTregs in humans are composed of populations with distinct cell surface display levels of ICOS (Ito et al 2008). Previous studies have shown that suppression of airway inflammation and AHR is associated with high levels of ICOS expression on CD4 + Tregs (Whitehead et al 2011) and that adoptive transfer of ICOS + CD4 + T cells, but not ICOS – cells, suppresses established AHR in mice (Shalaby et al 2012). We therefore compared numbers of ICOS + Foxp3 + Tregs, as well as the amount of ICOS on the cell surface of Tregs, in mice sensitized using 10 –3 or 10 –1 μg LPS.…”

“…Cell surface display levels of ICOS on Foxp3 + Tregs were also highest in mice sensitized using the suppressive dose of 10 –1 μg LPS. We did not directly compare the function of Tregs containing high and low levels of ICOS in the present study, but it has been previously observed that ICOS is required for suppression of allergic responses (Whitehead et al 2011) and that adoptive transfer of ICOS + CD4 + T cells suppresses airway eosinophilia and AHR, whereas transfer of ICOS – CD4 + T cells does not (Shalaby et al 2012). …”

Commensal microbes drive intestinal inflammation by IL-17–producing CD4 + T cells through ICOSL and OX40L costimulation in the absence of B7-1 and B7-2

“…Using mice eradicated of commensal bacteria, we also made the curious observation that re-establishing intestinal colonization with C. albicans alone does not induce ICOS expression by lamina propria CD4 + T cells. Whether this reflects discordant cell activation induced by C. ablicans compared with commensal enteric bacteria through TLR4 or NFAT that each promote CD4 + T-cell ICOS expression is uncertain, but represents an important area for future investigation (40,41).…”

The hygiene hypothesis in allergy and asthma

“…There are, however, numerous studies showing a protective effect of microbial components against the development of allergic inflammation in murine models. For example, Toll-like receptor (TLR) 9 agonists inhibit the development of asthma-like inflammation [37,38], and intranasal administration of TLR2/4 ligands has been tested as a potential protective vaccine against allergic airway inflammation [39]. Protection may not be elicited through only microbial components.…”