Varieties of acute immunologic damage to the rabbit lung

Organic dust toxic syndrome: an acute febrile reaction to organic dust exposure distinct from hypersensitivity pneumonitis

Organic dust toxic syndrome is a term recently coined to describe a noninfectious, febrile illness associated with chills, malaise, myalgia, a dry cough, dyspnea, headache and nausea which occurs after heavy organic dust exposure. Organic dust toxic syndrome shares many clinical features with acute farmer's lung and other forms of hypersensitivity pneumonitis, including the presence of increased numbers of neutrophils in bronchoalveolar lavage. However, organic dust toxic syndrome differs from acute hypersensitivity pneumonitis in several respects: the chest X-ray does not show infiltrates, severe hypoxemia does not occur, prior sensitization to antigens in the organic dust is not required and there are no known sequelae of physiological significance, such as the recurrent attacks and the pulmonary fibrosis which may be seen with chronic hypersensitivity pneumonitis. Organic dust toxic syndrome is thought to be much more common than farmer's lung. It is important for clinical and investigational purposes that organic dust toxic syndrome be distinguished from acute farmer's lung.

Pulmonary damage induced in mice by a monoclonal antibody to proteins associated with pig pulmonary surfactant

Severe pulmonary damage was induced in mice inoculated with hybridomas (8B5E) secreting a monoclonal antibody to the 15,000-dalton protein associated with pig pulmonary surfactant. These mice exhibited severe respiratory distress starting 8-9 days after inoculation and died. Microscopically, lungs were airless and congested with hyaline membrane formation in patent terminal airways. Purified antibody from this hybridoma also induced similar damage in mouse lungs. However, neither hybridomas (1B6A) nor purified antibody, which is specific to pig 35,000-dalton protein but not to the mouse counterpart, induced these changes. Electron microscopically, many unexpanded lamellar bodies were seen floating in the edema fluid in these damaged lungs, and fragmentary lipid membranes were found in the electron dense material around these lamellar bodies, suggesting disintegration of these structures. Alveolar epithelial cells were desquamated, leaving the basement membranes bare, and mouse C3 was demonstrated in the damaged lungs. This low-molecular-weight protein of mouse surfactant cross-reacted with this antibody in the immunoblotting method, and the antigen was located in the inclusions of alveolar wall cells. These observations indicate that this low-molecular-weight protein of mouse surfactant has an antigenic structure similar to pig surfactant protein and that antigen-antibody complex formation may have triggered the damage of the lungs through inactivation of surfactant and induction of immunological tissue damage.

Antigen-specific down-regulation of bronchial reactivity in rats sensitized daily without adjuvant

Daily sensitization with ovalbumin (OA) and dog serum albumin (DSA) without adjuvant was performed in rats for 2-week periods. When the antigen was administered subcutaneously (s.c.), antibody responses were induced, as assessed in serum and bronchial lavage, and strong increases in transpulmonary pressure (TPP) after intravenous (i.v.) challenge with antigen. Sensitization without adjuvant with antigen as aerosol for similar periods also evoked pronounced antibody formation, although only weak increases of TPP were seen after challenge. Animals sensitized s.c. with OA and simultaneously exposed to OA as aerosol exhibited suppression of the TPP increase after challenge, whereas the antibody responses were not affected to any great extent. In contrast, the increase of TPP after challenge in animals similarly sensitized s.c. with DSA were not suppressed by OA given simultaneously as aerosol or vice versa.

Hypersensitivity pneumonitis in rabbits. Modulation of pulmonary inflammation by long-term aerosol challenge with antigen

Immunized rabbits that were aerosol challenged for 2 to 3 wk with pigeon dropping extract, an etiologic agent of hypersensitivity pneumonitis, developed chronic pulmonary inflammation associated with cell-mediated immunity in bronchoalveolar cells. However, prolonged aerosol challenge for 12 wk resulted in the diminution of pulmonary inflammation (modulation) and the loss of demonstrable cell-mediated immunity. This was probably not due to loss of sensitized lymphocytes that mediated pulmonary inflammation. Furthermore, rabbits undergoing modulation when they were challenged with an unrelated antigen were refractory to the development of pulmonary inflammation for at least 9 wk. After this refractory period, animals reimmunized and aerosol challenged with pigeon dropping extract displayed an anamnestic response and produced pulmonary lesions that were strikingly similar to the histopathology of human hypersensitivity pneumonitis.

Antigen-specific densensitization in a rabbit model of acute hypersensitivity pneumonitis

Rabbits that had been prepared to develop acute alveolitis after aerosol challenge with simple protein antigens did not develop chronic alveolitis but rather gradually recovered despite continued challenge. Immunologic accompaniments of waning disease were compared in this model to those associated with intravenous injections of antigen causing "desensitization." We also studied the effects of aerosol challenge prior to systemic immunization, antigen specificity, and the duration of desensitization by aerosolized and intravenous antigen. We found that repeated aerosol or intravenous challenges produced antigen-specific desensitization in this model, and the effect lasted several weeks. Prior exposure to aerosolized antigen was not protective. Neither aerosol nor intravenous desensitization maneuvers abrogated antigen-specific lymphocyte blastogenesis, although an early transient fall did occur. Humoral responses were boosted. These findings suggest that chronic alveolitis is prevented in this model by specific desensitization, without the induction of true tolerance or of nonspecific anergy. Such immunoregulation may result from development of antigen-specific blockade or blocking factors (e.g., lymphokines), antigen-antibody complexes, or suppressor cells affecting specific effector cells. Evaluation of these mechanisms may have implications for diagnosis and prognosis in human hypersensitivity pneumonitis.

Amplification of the enzyme-linked immunosorbent assay (ELISA) in the detection of class-specific antibodies

A modification of the standard enzyme-linked immunosorbent assay (ELISA) is described which circumvents the requirement for specifically purified antibodies from which antibody-enzyme complexes are made. The assay utilizes the principle of a soluble anti-alkaline phosphatase immune complex (AP-A-AP) and has been called the amplified ELISA. Methods for preparing and evidence for the specificity of rabbit anti-rat gamma-FC, IgM (mu) and IgA (alpha) are presented. These reagents are used to measure anti-DNP antibodies belonging to classes IgG, IgM and IgA in rat serum. Using antiglobulin and anti-enzyme reagents prepared in guinea pigs, anti-ovalbumin antibodies are measured in rabbit serum. Titration curves are similar when the amplified ELISA is compared to the standard ELISA. A change in slope suggesting an effect of saturation of antigen sites, occurs at the same input antibody concentration for both assays. Determination of the anti-DNP concentration of unknown sera by extrapopulation from titration graphs of a known serum suggests that the value is overestimated, i.e., amplified when the amplified ELISA is used. In addition, the amplified ELISA has an improved ability to detect low levels of antibody. Evidence is presented which illustrates how the use of optimally conjugated DNP-proteins, age of conjugates, and optimal dilutions of secondary antiglobulins and the AP-A-AP reduce non-specific binding in the amplified ELISA. The amplified ELISA is capable of detecting 2.4 ng of antibody to ovalbumin in a one: one million dilution of rabbit serum with high reproducibility and low background.

Experimental leukocyte-induced pulmonary vasculitis with inquiry into mechanism

Intravenous transfusions of washed allogeneic or autologous leukocytes in rabbits resulted in lesions of pulmonary periarteritis 48 hours later. Intact leukocytes were required. Systemic anaphylaxis, generalized Shwartzman reaction, alternate pathway complement activation and inert particle microembolism failed to produce identical lesions. Leukocytes tagged with radioactive chromium were found within arterial thromboses with proximal vasculitis. Generation or release of inflammatory factors plus thromboembolism would explain the pathogenesis of the lesions described. Specific mechanisms may be quite complex. Similar lesions have not been described in studies of pulmonary leukocyte entrapment or experimental microembolism of the lung. This model may be useful for studying pathogenetic mechanisms in pulmonary vasculitis and may have clinical implications.

The role of precipitins and complement activation in the etiology of allergic lung disease

An experimental model of allergic lung disease has been described that is monitored by analysis of arterial oxygen tension following aerosol challenge with antigen. Rabbits immunized to a classical soluble antigen, human serum albumin (HSA), to the point where severe Arthus skin reactivity was demonstrable, were aerosol-challenged with antigen. Arterial oxygen tension measurements made on pre- and post-challenge samples yielded early, late, and continuous response patterns, reminiscent of those obtained in humans following provocation testing. Aerosol challenge of unimmunized animals with HSA resulted in no change from baseline conditions. Unimmunized rabbits exposed to small and massive (10X) aerosols of Aspergillus spores also demonstrated various postchallenge depressions in arterial oxygen tension as well as decreased levels in hemolytic complement activity, depending on the species of fungus and dose of spores used. Unimmunized animals pretreated with cobra venom factor in a manner known to achieve complement depletion failed to respond with altered arterial oxygen tensions following similar aerosol challenge. It is postulated that although precipitins may play a role in artificial disease initiated by soluble antigens, nonspecific complement activation may be more important in understanding the etiology of spontaneous disease in humans brought about by inhalation of moldy particulate matter.

Light and immunofluorescent study of the Arthus reaction in the rabbit lung

A localized Arthus reaction was produced in the lung of sensitized rabbits by delivery of antigen into a lower lobe bronchus using a method of selective bronchial catheterization under fluoroscopy. The rabbits were sensitized with bovine immunoglobulin G (B-IgG) in incomplete Freund's adjuvant (IFA) to produce precipitating antibody without classic delayed hypersensitivity. Pulmonary histopathology was studied at intervals following antigen challenge, using light and immunofluorescent microscopy. Gross lesions peripheral to the lower lobe bronchus receiving antigen were found within 12 hr. Subsequent necrosis resulted in a dense scar by 6 wk. Microscopically, early lesions were typified by localized bronchitis, bronchiolitis, alveolitis, and vasculitis with exuberant exudates containing predominantly polymorphonuclear leukocytes. Extensive focal necrosis was present by 72 hr. Immunofluorescent studies revealed the presence of B-IgG, rabbit IgG, and complement (C3) in and around bronchi, bronchioles, alveoli, and vessels. No granulomatous lesions were found, and proliferation of alveolar lining cells was not detected in these studies. Thus, the lung can participate in an acute Arthus reaction following local antigen challenge in systemically sensitized animals. The pathology more closely resembles a necrotizing bacterial pneumonia than an interstitial or hypersensitivity pneumonitis under the conditions of this experimental system. Implications for human disease are speculative.