Aerosol-induced immunoglobulin (Ig)-E unresponsiveness to ovalbumin does not require CD8+ or T cell receptor (TCR)-gamma/delta+ T cells or interferon (IFN)-gamma in a murine model of allergen sensitization

Abstract

Mice exposed for 20 min daily to aerosolized ovalbumin (OVA) for 10 d at concentrations from 1 to 0.01% OVA made greatly reduced immunoglobulin (Ig)-E responses to subsequent immunogenic OVA challenges, given either intraperitoneally or by aerosol. This IgE-specific unresponsiveness lasted for at least four months. However, these aerosol-treated mice were primed for larger OVA-specific IgG1 and IgG2a responses. The specific reduction in IgE responses was not due to preferential induction of a T helper (Th)-1 response as aerosol OVA- primed mice made greatly reduced Th2 and no detectable Th1 response after rechallenge in vitro. Consistent with this, the increase in circulating eosinophils observed in control Th2-primed mice was absent in aerosol OVA-treated animals. Interferon (IFN)-gamma was not required for this unresponsiveness, as IFN-gamma knockout mice and anti-IFN-gamma antibody-treated wild-type mice had greatly reduced levels of IgE similar to wild-type controls. CD8+ T cells played a relatively small role as IgE responses were reduced to about the same extent in beta2 microglobulin-deficient, or in anti-CD8-treated wild-type mice as in normal mice after aerosol OVA treatment. Similarly, T cell receptor (TCR)-gamma/delta T cells were not required for maximal inhibition of the IgE response. These results demonstrate that exposure to inhaled protein antigens can induce a state of unresponsiveness of CD4+ T cells that results in a prolonged loss of IgE and eosinophil responses to subsequent challenges. This T cell unresponsiveness was shown not to require CD8+ or TCR-gamma/delta+ T cells or IFN-gamma.

Figure 1

IgE, IgG1, and IgG2a anti-OVA antibody production in BALB/c mice after exposure to OVA. Naive BALB/c mice were primed by exposing them to aerosolized OVA for 10 d, beginning at day 0. The concentration of the OVA administered was 1%, 0.1%, 0.01%, 0.001%, or PBS. At day 27, all groups were challenged with an intraperitoneal injection of 10 μg OVA/AL and on day 120, they were exposed to 1% aerosolized OVA for 20 min. Mice were bled from their tail veins on day 50 and 131. OVA-specific antibodies were estimated by ELISA and expressed as mean ± SEM.

Figure 1

IgE, IgG1, and IgG2a anti-OVA antibody production in BALB/c mice after exposure to OVA. Naive BALB/c mice were primed by exposing them to aerosolized OVA for 10 d, beginning at day 0. The concentration of the OVA administered was 1%, 0.1%, 0.01%, 0.001%, or PBS. At day 27, all groups were challenged with an intraperitoneal injection of 10 μg OVA/AL and on day 120, they were exposed to 1% aerosolized OVA for 20 min. Mice were bled from their tail veins on day 50 and 131. OVA-specific antibodies were estimated by ELISA and expressed as mean ± SEM.

Figure 2

Measurement of OVA in the lung of  BALB/c mice after 20 min of exposure to aerosolized OVA. Mice (5–10 mice per group) were exposed to aerosolized OVA at concentrations from 1 to 0.001%. Lungs were removed immediately, placed on a wire mesh, minced, and then suspended in 10 ml of RPMI. Suspension was centrifuged and supernatant assayed by ELISA for OVA.

Figure 3

Blood eosinophils in OVA-sensitized mice. □, Wild-type, , β₂m−/−, and ▪, IFN-γ−/− BALB/c mice were bled from the tail vein on day 4 after the tertiary exposure and the eosinophils were counted in Discombe's fluid on a hemacytometer (18). Data represent the mean (± SEM) eosinophil counts per milliliter in groups of five mice.