Patrick G. Holt

Sublingual allergen administration. I. Selective suppression of IgE production in rats by high allergen doses

Sublingual administration of a protein allergen to immunologically naïve rats suppressed subsequent allergen‐specific IgE responses. Susceptibility to this form of immunotherapy was genetically determined, with some inbred rat strains displaying immunological tolerance in the IgE antibody class alone, whilst others developed concomitant suppression of IgG. Parallel gastric intubation experiments established that the development of tolerance by sublingual allergen administration proceeded independently of events occurring in the gut resulting from swallowing the allergen. These results are consistent with clinical reports which suggest that the oral mucosa is a potentially useful site for therapeutic modulation of allergic reactivity, and indicate that appropriate animal models can be developed to probe this important question. However, further research is required to determine the relevance of these findings to current sublingual desensitization practices.

Effect of Influenza Virus Infection on Allergic Sensitization to Inhaled Antigen in Mice

Repeated exposure of healthy mice to an aerosol of ovalbumin (OA) leads to the development of IgE-isotype-specific immunological tolerance. However, when initial OA exposure occurs during the acute phase of influenza infection, tolerance does not occur, and the mice instead develop high titres of OA-specific IgE in response to subsequent challenge with the allergen.

Tolerance Induction via Antigen Inhalation: Isotype Specificity, Stability, and Involvement of Suppressor T Cells

Mice were exposed to aerosolized ovalbumin (OA) once weekly for 5 min on 6 occasions, prior to systemic challenge with soluble or alum-adsorbed (AH-OA) antigen. Mice challenged with AH-OA manifested profound IgE isotype-specific tolerance; those challenged with soluble OA initially manifested anamnestic IgE/IgG responses, but secondary intraperitoneal immunization 13 days later with soluble OA revealed IgE isotype-specific tolerance. The tolerized mice contained splenic suppressor T cells which inhibited IgE but not IgG responses in an adoptive transfer assay. Tolerance was still demonstrable in mice 6 months after the cessation of aerosol exposures. Exposure of low IgE responder rat strains to aerosolized OA tolerized for both IgE and IgG responses.

Alveolar macrophages: IV. Interspecies differences in activity in proliferating lymphocyte cultures☆

Abstract Alveolar macrophages (AM) were collected by repeated endobronchial lavage from mice, rats, guinea pigs, and rabbits, and titrated into cultures of mitogen-stimulated syngeneic or autochthonous lymphocytes. Significant species differences were detected in regard to AM activity in the cultures. AM from guinea pigs and mice stimulated PHA-induced lymphoproliferation, while those from rats and rabbits were inhibitory; blood or peritoneal macrophages were not inhibitory in any of the species examined.

Adoptive Transfer of ‘Persistent’ IgE Responses in Mice in the Absence of Secondary Antigenic Stimulation

Spleen cells were prepared from Balb/c mice immunized 30 days previously with alum-precipitated ovalbumin (OA), which manifested high, persistent titres of anti-OA IgE and IgG. The adoptive transfer of 5.0 X 10(7) such cells to X-irradiated syngeneic recipients produced comparable persistent IgE/IgG responses, in the absence of secondary antigenic challenge. Fractionation procedures indicated that the nylon-wool adherent population from the spleen was the most active in effecting transfer of the response. However, donor T-cells were also required, as pretreatment of the cellular inoculum with anti-Thy 1.2 antiserum ablated transfer. The inclusion of serum containing anti-OA IgG (but not IgE) in the cellular inoculum also blocked the transfer.

The role of the thymus in the maintenance of natural killer cells in vivo

This report describes a model for investigating the role of the thymus in regulating natural killer (NK) cell activity in vivo. Evidence is presented that the thymus can regulate NK cells, and that at least some NK cells can develop without thymic help. Marrow from thymectomized rats depleted of circulating T cells by thoracic duct cannulation was transplanted into rats without a thymus (1 degree ATX.BM). These 1 degree ATX.BM rats had NK cell levels above controls 3 months after reconstitution but markedly depressed NK cell levels by 9 months. When 1 degree ATX.BM marrow was used to reconstitute rats with or without a thymus, those without a thymus (2 degrees ATX.BM) exhibited low NK cell levels after 3 months, and a similar result was obtained when 2 degrees ATX.BM marrow was used to reconstitute 3 degrees ATX.BM rats. The low NK cell levels in 2 degrees and 3 degrees ATX.BM rats were due to a deficiency in spontaneously cytotoxic NK cells, as they had normal numbers of interferon-responsive pre-NK cells. Spleen cells from 2 degrees and 3 degrees ATX.BM rats produced less interferon than control spleen cells when cultured with P815 tumor cells in vitro. However, 2 degrees and 3 degrees ATX.BM rats had higher numbers of large granular lymphocytes than controls despite their low NK cell levels. In marked contrast to 2 degrees and 3 degrees ATX.BM rats, spleen cells from 4 degrees ATX.BM rats had higher levels of cytotoxicity and a higher frequency of both spontaneously cytotoxic and pre-NK cells than controls. The 4 degrees ATX.BM rats also had the highest frequency of large granular lymphocytes in the spleen.

In vivo Arming of Cutaneous Mast Cell Receptors by IgE Released from Macrophages

Intracutaneous injection of purified peritoneal macrophages harvested from ovalbumin (OVA)-hypersensitive high-IgE-responder BN rats into naive animals sensitised the injection sites for subsequent OVA-specific passive cutaneous anaphylaxis (PCA) reactions. The underlying mechanism(s) were investigated using a macrophage cell line (WEHI 265.1), which exhibited comparable sensitising activity in rat or mouse skin, after initial pulsing in vitro with antiserum rich in OVA-specific IgE. Transfer of OVA-hypersensitivity by the cell line (1) was IgE-dependent and did not occur when the cells were pre-exposed to antiserum containing OVA-specific IgG alone, (2) was blockable by saturation of cell surface receptors in the recipient with myeloma IgE (but not myeloma IgG), and (3) did not occur in mast cell-deficient mice carrying the W/Wv mutation, in contrast to their normal heterozygous littermates which developed marked OVA-hypersensitivity at the injection site. These results are consistent with arming of IgE-receptors on cutaneous mast cells by IgE antibody released from macrophages, and hint at a possible role for phagocytes in amplifying IgE-mediated reactions in tissues.

Macrophage Regulation of the IgE Response

The ability of macrophage-associated antigen to both prime for, and subsequently trigger, IgE responses in inbred rats and mice was investigated. Peritoneal exudate cells briefly pulsed in vi