ANIMAL MODEL OF HUMAN DISEASE
Chronic Bronchitis Animal Model: Enzootic Pneumonia of Swine. Bronchial Gland Hvpertrophy Induced by Isoprenaline
Contributed by: A. Baskerville, BVSc, PhD, MRCVS, MRCPath, Microbiological Research Establishment, Porton Down, Salisbury, Wilts, England.
Bioogic Features
Human chronic bronchitis is a common and debilitating condition v-hich results in hvpersecretion of mucus by the bronchial submucosal glands and to a lesser extent by goblet cells in the bronchial epithelium. The basic pathologic change in chronic bronchitis is hypertrophv of the bronchial submucosal glands and increased production of mucus.' A convenient and accurate measurement of the presence and degree of this hxpertrophv in necropsv material is bv calculation, from histologic sections. of the ratio of the thickness of these glands in relation to the thickness of the entire bronchial wall. This ratio is often known as the gland-to-w-all ratio or Reid index.2 The animal used most commonly for experimental study of chronic bronchitis is the rat, since the bronchi of most other laboratory animals, domestic animals, and nonhuman primates either completely lack submucosal glands or have glands which are extremely poorly developed. The changes of chronic bronchitis can be successfully induced in the tracheobronchial glands of the rat 3 and in the sparse bronchial glands of the dog 4 by exposure to irritant gases. These svstems provide much valuable pathologic information on mucus secretion and chronic bronchitis, though they do have the disadvantage that some parameters used in man, such as the gland-to-wall ratio, cannot be applied to them. Usefulness of the Model
It is now- becoming apparent that the pig can be used as an additional animal model for research into chronic bronchitis. A histologic Publication sponsored by the Registry of Comparative Pathology of the Armed Forces Institute of Pathology and supported bh Public Health Serv ice Grant RR 0301 from the Disision of Research Resources. L-S Department of Health. Education and Welfare. under the auspices of U nisersities Xssociated for Research and Education in Pathology. Inc 237
238
BASKERVILLE
American Journal of Pathology
comparison of the bronchial glands of man and of seven animal species 5 show-ed that the pig has submucosal glands which compare most closely in degree of development and distribution with those of man, since they are large and occupy much of the circumference of the bronchus (Figure 1). The pig also suffers commonly from a chronic bronchitis and pneumonia know n as enzootic pneumonia which is caused by infection with intrapulmonary mv-coplasmas.6 Affected pigs cough persistentlk. exhibit
i V# PW ,t4-mLqo,.
:.,..
IL
Iwo
11
I * 'N
-AS
-.
0
IF-,
..
.:".,.
-E:
wz::,.::::
Figure 1-Bronchus of normal 2-month-old pig showing well-developed submucosal mucous glands and goblet cells in the epithelium. (Combined Alcian blue, pH 2.6. and periodic acid-Schiff staining. x 185).
labored respiratoru- movements, and have reduced exercise tolerance, all of Xwhich are clinical characteristics of human chronic bronchitis. It has been found recently that one of the major pathologic features of enzootic pneumonia is hvpertrophy of the bronchial submucosal glands 8 accompanied by hypersecretion of mucus and accumulation of mucoid or mucopurulent secretion in the airways. The normal pig has a gland-tow-all ratio of 0.2.5 to 0:37.8 a range similar to that of the inormal lhtnmai adult (0.14 to 0.36).2 These facts suggested that the pig is a suitable subject for experimental production of bronchial gland hypertrophy with some relevance to the human disease. Enzootic pneumonia can be readily reproduced experimentally, and progressive hvpertrophv of the submucosal glands develops from as early as 9 days after infection; examination of field cases suggests that it persists for many months.8 The gland w all ratios in these animals (0.40 to 0.56) are comparable to those reported in human patients with chronic bronchitis (0.41 to O0.9).2
Vol. 82, No. 1 January 1976
CHRONIC BRONCHITIS
239
I
Figure 2-Bronchial gland hypertrophy and increase in number of goblet cells in the epithelium after isoprenaline in a section stained in the same manner as Figure 1 (x 185).
Recent histochemical studies on the lungs of normal pigs and pigs with experimentally produced enzootic pneumonia have shown that there is a striking similarity between the normal glvcoprotein composition of the bronchial glands of pig and man, and also in the changes in glycoprotein content which occur in human chronic bronchitis and in enzootic pneumonia.9'0 In both species, mucous and serous cells in the bronchial glands increase in number and size, there is an increase in acid glxycoprotein production relative to neutral, and an increase in sulfomucin. Enzootic pneumonia in pigs apparently provides the first proven instance of a direct association betwveen infection and bronchial submucosal gland hypertrophy, a relationship frequently suspected in man. Recent studies show that bronchial gland hypertrophy also occurs in pulmonary infection in pigs with the bacteria Salmonella choleraesuis, Pasteurella niultocida and Haemophilus influenzae-suis." It is possible that work on these bacterial and mycoplasmal infections will eventually shed some light on the mechanisms by which the mucous gland hypertrophv is brought about. A disadvantage of measuring changes produced by an infectious process in vivo is that the infection cannot be completely arrested when required, even by antibiotic therapy. Reproduction of the changes of chronic bronchitis by drugs overcomes this. Sturgess and Reid 12 employed the sympathomimetic and parasympathomimetic amines isoprenaline and pilocarpine to produce hypertrophy of the tracheal glands
240
BASKERVILLE
American Journal of Pathology
and an increase in goblet cell numbers in the rat. These drugs have recentlI been used in the pig 13 in which isoprenaline was found to reproduce closelv the changes of chronic bronchitis, with striking bronchial submucosal gland hypertrophy and increase in the number of goblet cells in the epithelium (Figure 2). The pig is therefore an extremely valuable animal for research into those diseases which are characterized bv hy"persecretion of altered mucus in the lungs such as chronic bronchitis and cystic fibrosis. Its usefulness is further enhanced by having lungs similar in size and capacity to those of man and by its being suitable for the performance of certain studies of pulmonary function. Availability
Swine are readily available, and bronchial gland hypertrophy can be produced readily with isoprenaline. References 1. Reid L: Pathology of chronic bronchitis. Lancet 1:275-278, 1954 2. Reid L: Measurement of the bronchial mucous gland layer: A diagnostic yardstick in chronic bronchitis. Thorax 15:132-141, 1960 3. Jones R, Bolduc P, Reid L: Goblet cell glycoprotein and tracheal gland hypertrophy in rat airways: The effect of tobacco smoke with or without the anti-inflammatoryagent phenvlmethyloxadiazole. Br J Exp Pathol, 54:229-239, 1973 4. Chakrin LW\', Saunders LZ: Experimental chronic bronchitis: Pathology in the dog. Lab Invest 30:143-154, 1974 5. Goco RV, Kress MB: Brantigan OC: Comparison of mucus glands in the tracheobronchial tree of man and animals. Ann NY Acad Sci 106:555-571, 1963 6. Goodwin RFWN7, Pomeroy AP, Whittlestone P: Production of enzootic pneumonia in pigs with a mycoplasma. Vet Rec 77:1247, 1965 Gois NI, V'alicek L, Sovadina N: Mycoplasma hyorhinis, a causative agent of pig pneumonia. Zentralbl V-eterinaermed [B]15 :230-240, 1968 8. Baskerville A: Development of the early lesions in experimental enzootic pneumonia of pigs: An ultrastructural and histological study. Res Vet Sci 13:570-578, 1972 9. Jones R. Baskerville A, Reid L: Histochemical identification of glycoproteins in pig bronchial epithelium: a) normal and b) hypertrophied from enzootic pneumonia. J Pathol 116:1-11. 1975 10. Lamb D, Reid L: Histochemical types of acidic glycoprotein produced by mucous cells of the tracheobronchial glands in man. J Pathol 9S:213-229. 1969 11. Baskerville A: Unpublished data 12. Sturgess J, Reid L: The effect of isoprenaline and pilocarpine on (a) bronchial mucus-secreting tissue and (b) pancreas, salivary glands, heart, thymus, liver and spleen. Br J Exp Pathol 54:388-403. 1973 13. Baskerville A: In press
Chronic Bronchitis Animal Model: Enzootic Pneumonia of Swine. Bronchial Gland Hvpertrophy Induced by Isoprenaline
Contributed by: A. Baskerville, BVSc, PhD, MRCVS, MRCPath, Microbiological Research Establishment, Porton Down, Salisbury, Wilts, England.
Bioogic Features
Human chronic bronchitis is a common and debilitating condition v-hich results in hvpersecretion of mucus by the bronchial submucosal glands and to a lesser extent by goblet cells in the bronchial epithelium. The basic pathologic change in chronic bronchitis is hypertrophv of the bronchial submucosal glands and increased production of mucus.' A convenient and accurate measurement of the presence and degree of this hxpertrophv in necropsv material is bv calculation, from histologic sections. of the ratio of the thickness of these glands in relation to the thickness of the entire bronchial wall. This ratio is often known as the gland-to-w-all ratio or Reid index.2 The animal used most commonly for experimental study of chronic bronchitis is the rat, since the bronchi of most other laboratory animals, domestic animals, and nonhuman primates either completely lack submucosal glands or have glands which are extremely poorly developed. The changes of chronic bronchitis can be successfully induced in the tracheobronchial glands of the rat 3 and in the sparse bronchial glands of the dog 4 by exposure to irritant gases. These svstems provide much valuable pathologic information on mucus secretion and chronic bronchitis, though they do have the disadvantage that some parameters used in man, such as the gland-to-wall ratio, cannot be applied to them. Usefulness of the Model
It is now- becoming apparent that the pig can be used as an additional animal model for research into chronic bronchitis. A histologic Publication sponsored by the Registry of Comparative Pathology of the Armed Forces Institute of Pathology and supported bh Public Health Serv ice Grant RR 0301 from the Disision of Research Resources. L-S Department of Health. Education and Welfare. under the auspices of U nisersities Xssociated for Research and Education in Pathology. Inc 237
238
BASKERVILLE
American Journal of Pathology
comparison of the bronchial glands of man and of seven animal species 5 show-ed that the pig has submucosal glands which compare most closely in degree of development and distribution with those of man, since they are large and occupy much of the circumference of the bronchus (Figure 1). The pig also suffers commonly from a chronic bronchitis and pneumonia know n as enzootic pneumonia which is caused by infection with intrapulmonary mv-coplasmas.6 Affected pigs cough persistentlk. exhibit
i V# PW ,t4-mLqo,.
:.,..
IL
Iwo
11
I * 'N
-AS
-.
0
IF-,
..
.:".,.
-E:
wz::,.::::
Figure 1-Bronchus of normal 2-month-old pig showing well-developed submucosal mucous glands and goblet cells in the epithelium. (Combined Alcian blue, pH 2.6. and periodic acid-Schiff staining. x 185).
labored respiratoru- movements, and have reduced exercise tolerance, all of Xwhich are clinical characteristics of human chronic bronchitis. It has been found recently that one of the major pathologic features of enzootic pneumonia is hvpertrophy of the bronchial submucosal glands 8 accompanied by hypersecretion of mucus and accumulation of mucoid or mucopurulent secretion in the airways. The normal pig has a gland-tow-all ratio of 0.2.5 to 0:37.8 a range similar to that of the inormal lhtnmai adult (0.14 to 0.36).2 These facts suggested that the pig is a suitable subject for experimental production of bronchial gland hypertrophy with some relevance to the human disease. Enzootic pneumonia can be readily reproduced experimentally, and progressive hvpertrophv of the submucosal glands develops from as early as 9 days after infection; examination of field cases suggests that it persists for many months.8 The gland w all ratios in these animals (0.40 to 0.56) are comparable to those reported in human patients with chronic bronchitis (0.41 to O0.9).2
Vol. 82, No. 1 January 1976
CHRONIC BRONCHITIS
239
I
Figure 2-Bronchial gland hypertrophy and increase in number of goblet cells in the epithelium after isoprenaline in a section stained in the same manner as Figure 1 (x 185).
Recent histochemical studies on the lungs of normal pigs and pigs with experimentally produced enzootic pneumonia have shown that there is a striking similarity between the normal glvcoprotein composition of the bronchial glands of pig and man, and also in the changes in glycoprotein content which occur in human chronic bronchitis and in enzootic pneumonia.9'0 In both species, mucous and serous cells in the bronchial glands increase in number and size, there is an increase in acid glxycoprotein production relative to neutral, and an increase in sulfomucin. Enzootic pneumonia in pigs apparently provides the first proven instance of a direct association betwveen infection and bronchial submucosal gland hypertrophy, a relationship frequently suspected in man. Recent studies show that bronchial gland hypertrophy also occurs in pulmonary infection in pigs with the bacteria Salmonella choleraesuis, Pasteurella niultocida and Haemophilus influenzae-suis." It is possible that work on these bacterial and mycoplasmal infections will eventually shed some light on the mechanisms by which the mucous gland hypertrophv is brought about. A disadvantage of measuring changes produced by an infectious process in vivo is that the infection cannot be completely arrested when required, even by antibiotic therapy. Reproduction of the changes of chronic bronchitis by drugs overcomes this. Sturgess and Reid 12 employed the sympathomimetic and parasympathomimetic amines isoprenaline and pilocarpine to produce hypertrophy of the tracheal glands
240
BASKERVILLE
American Journal of Pathology
and an increase in goblet cell numbers in the rat. These drugs have recentlI been used in the pig 13 in which isoprenaline was found to reproduce closelv the changes of chronic bronchitis, with striking bronchial submucosal gland hypertrophy and increase in the number of goblet cells in the epithelium (Figure 2). The pig is therefore an extremely valuable animal for research into those diseases which are characterized bv hy"persecretion of altered mucus in the lungs such as chronic bronchitis and cystic fibrosis. Its usefulness is further enhanced by having lungs similar in size and capacity to those of man and by its being suitable for the performance of certain studies of pulmonary function. Availability
Swine are readily available, and bronchial gland hypertrophy can be produced readily with isoprenaline. References 1. Reid L: Pathology of chronic bronchitis. Lancet 1:275-278, 1954 2. Reid L: Measurement of the bronchial mucous gland layer: A diagnostic yardstick in chronic bronchitis. Thorax 15:132-141, 1960 3. Jones R, Bolduc P, Reid L: Goblet cell glycoprotein and tracheal gland hypertrophy in rat airways: The effect of tobacco smoke with or without the anti-inflammatoryagent phenvlmethyloxadiazole. Br J Exp Pathol, 54:229-239, 1973 4. Chakrin LW\', Saunders LZ: Experimental chronic bronchitis: Pathology in the dog. Lab Invest 30:143-154, 1974 5. Goco RV, Kress MB: Brantigan OC: Comparison of mucus glands in the tracheobronchial tree of man and animals. Ann NY Acad Sci 106:555-571, 1963 6. Goodwin RFWN7, Pomeroy AP, Whittlestone P: Production of enzootic pneumonia in pigs with a mycoplasma. Vet Rec 77:1247, 1965 Gois NI, V'alicek L, Sovadina N: Mycoplasma hyorhinis, a causative agent of pig pneumonia. Zentralbl V-eterinaermed [B]15 :230-240, 1968 8. Baskerville A: Development of the early lesions in experimental enzootic pneumonia of pigs: An ultrastructural and histological study. Res Vet Sci 13:570-578, 1972 9. Jones R. Baskerville A, Reid L: Histochemical identification of glycoproteins in pig bronchial epithelium: a) normal and b) hypertrophied from enzootic pneumonia. J Pathol 116:1-11. 1975 10. Lamb D, Reid L: Histochemical types of acidic glycoprotein produced by mucous cells of the tracheobronchial glands in man. J Pathol 9S:213-229. 1969 11. Baskerville A: Unpublished data 12. Sturgess J, Reid L: The effect of isoprenaline and pilocarpine on (a) bronchial mucus-secreting tissue and (b) pancreas, salivary glands, heart, thymus, liver and spleen. Br J Exp Pathol 54:388-403. 1973 13. Baskerville A: In press
