Immunoregulation in atopic dermatitis: functional analysis of T-B cell interactions and the enumeration of Fc receptor-bearing T cells

Virus associated immune and pharmacologic mechanisms in disorders of respiratory and cutaneous atopy

Anaphylaxis represents non-atopic immediate hypersensitivity, whereas manifestations of atopic immediate hypersensitivity include bronchial asthma, hay fever, allergic rhinitis, chronic urticaria, and atopic dermatitis. In spite similar antigen exposure, only a minority of the population shown some form of atopic disease. Atopic disease with its spontaneous pattern of familial occurrence cannot be induced at will.

The exact pathogenesis of atopy is yet to be elucidated. Two theories prevail: 1) atopy is a primary disorder of the immune system with sequelae in the various effector tissues; and 2) a concept of atopy as a primary autonomic imbalance, essentially beta adrenergic in character, with sequelae in effector cells, including those engaged in the production of antibodies. The autonomic imbalance is perceived as caused not by some disorder of the autonomic nervous system itself but by a defector functioning of its effector cells. These two concepts are not mutually exclusive. The IgE antibody, which mediates allergic reactions, is essentially identical with atopic reagin in various animal species.

The beta adrenergic theory regards atopic disorders (i.e., perennial and seasonal allergic rhinitis, bronchial asthma, and atopic dermatitis) not as immunologic diseases but as unique patterns of altered reactivities to a broad spectrum of immunologic, psychic, infectious, chemical and physical stimuli. The antigen-antibody interaction is given the same role as that of a broad category of nonspecific stimuli that function only to trigger the same defective homeostatic mechanism in the various effector cells involved in immediate hypersensitivities. Current evidence favors the possibility that there are inherited and/or acquired multiple abnormalities in the receptor—adenylate cyclase—cyclic AMP system of all effector cells that are critical in the organization of immune reactivities.

Atopic abnormality may be 1) acquired by functional receptor regulatory shifts caused by hormonal changes, infection (viral, bacterial, etc), allergic tissue injury or other event; 2) genetically determined; or 3) caused by autoimmune disease. One, two or all three of these effector mechanisms may be operative in a particular disease.

There is an important relationship between asthma and viral respiratory infection. A history of childhood viral respiratory illness is a risk factor for the development of chronic obstructive airway syndromes in later life. Asthmatic attacks occurred only when the infection produced fever, malaise, cough or coryza. The dominant role of fever in these episodes immediately suggests the profound involvement of adrenergic effector mechanisms. The presence of autoantibodies to beta-adrenoceptors in patients correlated well with a reduced beta—and an increased alpha-adrenergic responsiveness. Virus infections can elicit autoantibody formation.

In patients with atopic dermatitis an increased susceptibility and abnormal host response to viral infections in general. Defective cytotoxic T cells, abnormally functioning macrophages and natural killer cells, a reduced production of IFNα in children, and of IFNγ in atopic patients with food allergy has recently been demonstrated. Lymphocytic cyclic AMP-phosphodiesterase, that destroys cyclic AMP, is increased in atopic dermatitis and in allergic respiratory disease of adults, and this increased activity correlated closely with histamine release from basophils. Peripheral blood leukocytes and lymphocytes in atopic dermatitis have frequently demonstrated impaired beta adrenergic reactivity.

Allergic tissue injury may be initiated by antigen-specific IgE antibodies that combine with Fcε receptors on various cell types and trigger mediator release upon encounter with the antigen. Various noxious agents that are capable of triggering asthma are capable of releasing inflammatory mediators from the same target cells. Accounting only for those pharmacologic mediators where the cell-type has been identified, the spectrum of mediator-storing, synthesizing, or transporting cells includes neutrophil leucocytes, basophilic leucocytes eosinophilic leucocytes; mast cells, “chromaffin-positive” mast cells, enterochromaffin cells, chromaffin cells; platelets, neurosecretory cells and nerve cells that potentially produce all amine-mediators as well as prostaglandins and kinins.

Altered spontaneous and histamine-induced in vitro suppressor-cell function in dogs with atopic dermatitis

Spontaneous, histamine-induced and Concanavalin A (Con A)-induced suppression of Con A mitogenesis of autologous responder cells was studied in normal dogs and in dogs with atopic dermatitis. Histamine-induced suppression was significantly decreased in the atopic dogs, as was the Con A-induced suppression, at supraoptimal concentration of Con A, to a lesser extent. Total numbers of histamine type 1 or type 2 receptors were not different for cells from atopic or normal dogs. The spontaneous suppression was significantly greater for the atopic dogs and this was not accounted for by the effect of non-specific dermatitis, increased macrophage-induced suppression or increased induction by mitogenic factors in the culture medium. Some possible mechanisms for these results are discussed, and the similarities to suppressor cell function in humans with atopic disease are noted.

In vivo and in vitro effects of glucocorticoids on lectin-induced blastogenesis in atopic dermatitis

The effects of glucocorticoids administered in vivo and in vitro on lectin-induced proliferation of lymphocytes sampled from venous blood were investigated in patients with atopic dermatitis (AD) and in normal controls. Stimulation by concanavalin A (Con A), phytohaemagglutinin A (PHA) and pokeweed mitogen (PWM) in patients and controls did not differ significantly under baseline conditions. After in vivo administration of methylprednisolone the decline of Con A-induced blastogenesis of leucocytes was similar in both groups, whereas PHA stimulation caused a significant reduction in the controls only. In vitro addition of different dexamethasone concentrations had a pronounced suppressive effect on Con A- and PHA-induced blastogenesis in both groups, whereas PWM stimulation was unaffected. Pretreatment in vivo with methylprednisolone further decreased the suppression of the Con A and PHA lymphocyte proliferation rate by dexamethasone added in vitro in controls but not in patients. With regard to B-cell proliferation generated by PWM, no consistent glucocorticoid effect could be observed. The impaired effect on lymphocyte blastogenesis of glucocorticoids administered in vivo, in contrast to a normal in vitro reaction to dexamethasone, together with recent findings of an altered glucocorticoid receptor pharmacology in AD, points to a decreased biological in vivo efficiency of methylprednisolone in atopic dermatitis.

Leukotriene B4 in atopic dermatitis: increased skin levels and altered sensitivity of peripheral blood T-cells

Employing a radioimmunoassay, de-proteinated suction blister fluid from 12 patients with active atopic dermatitis appeared to contain higher levels of the pro-inflammatory and immunomodulatory mediator leukotriene B4 (LTB4) than suction blister fluid from 12 non-atopic individuals. Indirect support for the identity of the mediator was obtained by HPLC of pooled samples. Nylon wool enriched T cells from six patients with atopic dermatitis and six non-atopic people preincubated with LTB4 (10(-10) M - 10(-8) M) expressed no statistically significant suppression in co-culture with mitogen stimulated autologous mononuclear cells, and there was no difference between atopic and non-atopic T cells in this respect. In contrast, LTB4 induced a dose-dependent reduction in the percentage of phenotypic Leu 2a (suppressor) cells leading to an increased helper/suppressor ratio in five atopic patients that was not observed in five non-atopics. Elevated skin levels of LTB4 may initiate or amplify dermal inflammation, and abnormal T cell response to the mediator may account for the increased helper/suppressor ratio characteristic of patients with atopic dermatitis.

T cell responses in allergic rhinitis, asthma and atopic dermatitis

Although clinical responses to allergens have been shown to primarily involve IgE antibodies, there is often no clear correlation between the amount of allergen-specific IgE present in the serum and the nature and severity of allergic symptoms. This observation raises the question of the possible role of non-IgE mediated types of immune responses in this reaction. It is not known to what extent components of T cell-mediated immunity are involved in IgE-mediated reactions but several observations suggest an association between atopic disease and alterations in cellular immune function. These include the frequent association of high serum IgE levels with: (i) several of the primary and acquired immunodeficiencies characterized by partial T cell deficiency; (ii) the defective cell-mediated immunity and resultant recurrent infections seen in the hyper-IgE syndrome; and (iii) the sudden rise in serum IgE levels associated with reduced numbers of suppressor T cells in bone marrow transplant recipients during the acute graft vs host disease. In this review, we will examine the recent evidence suggesting that the T lymphocyte may play a primary role in the pathogenesis of atopic disorders.

Phosphodiesterase inhibition by Ro 20-1724 reduces hyper-IgE synthesis by atopic dermatitis cells in vitro

Peripheral blood mononuclear leukocytes (MNL) from patients with atopic dermatitis spontaneously produce large amounts of IgE in vitro. These cells also show markedly elevated levels of cAMP phosphodiesterase (PDE) which may be responsible for the observed abnormal cAMP responsiveness. Treatment of atopic dermatitis MNL with varying concentrations of the cAMP PDE inhibitor Ro 20-1724 resulted in progressively decreasing amounts of IgE synthesis, statistically significant at the 10(-4) M and 10(-5) M concentrations. There was a close correlation between PDE inhibition and inhibition of IgE synthesis, r = 0.93, p less than 0.05. To define the cellular target of the drug, we used monoclonal antibodies directed toward MNL subsets (Lyt 3, OKT8, OKT4, monocyte-myeloid) in a modified "panning" method to perform experiments with purified subsets. With untreated subsets, removal of OKT4-positive cells significantly reduced IgE synthesis; readdition of OKT4-positive cells enhanced IgE synthesis. OKT8 cells and monocytes did not affect IgE synthesis. Pretreatment of T cell-depleted MNL with Ro 20-1724 resulted in significantly more inhibition of IgE synthesis than did pretreatment of T enriched cells prior to recombination with the reciprocal untreated subset and subsequent culture. Similarly, pretreatment of monocyte-depleted cells resulted in significantly more inhibition of IgE synthesis than pretreatment of monocyte-enriched cells prior to recombination and culture. The majority of the effect appeared to be mediated by a direct effect on the B cells. However, some inhibition of IgE synthesis was also achieved through pretreatment of T enriched cells. Since pretreatment of isolated suppressor/cytotoxic or helper/inducer T-cell subsets did not give the same degree of inhibition as with unfractionated T cells, a T-T interaction may be involved in this aspect. The imidazolidinone derivative, Ro 20-1724, significantly and consistently inhibited both the elevated cAMP phosphodiesterase activity and the elevated spontaneous IgE synthesis of MNL from patients with atopic dermatitis. These findings demonstrate a previously undescribed link between cAMP PDE levels and in vitro IgE synthesis.

Natural-killer-cell activity in atopic dermatitis

Natural-killer (NK)-cell activity was measured in the peripheral blood of twenty patients with atopic dermatitis and in a group of thirteen age-matched non-atopic controls (nine subjects on thirteen occasions). The method uses a chromium-release assay with the human leukaemia cell line, K562, labelled with 51Cr as the target cell. A highly significant reduction in NK-cell activity was found in the patients with atopic dermatitis.

Atopic dermatitis. Special clinical complications

Atopic dermatitis is a common disease of childhood that remits with age. Its pathogenesis is still uncertain; histamine seems important but the role of IgE is uncertain. The condition presents with several clinical features, none of which alone is pathognomonic. In some patients, particularly infants, several observations may be needed to discover the chronic nature of the disease. Most patients with atopic dermatitis have excessive skin dryness and hand dermatitis; many have superficial pustular staphylococcal infection. Management focuses on measures that reduce trigger factors, such as skin irritant exposure, emotional stress, and infection. Therapeutic agents include emollient creams, corticosteroid creams and ointments, and oral antihistamines. Exposure to summer sunshine is important in control.