The aim of this study is to record the age related histological and involutory changes of bursa of Fabricius in guinea fowl. The samples were collected from different age groups of birds from day-old to six months at monthly interval. The tissues of bursa of Fabricius were fixed in 10 per cent neutral buffered formalin and Bouin’s fluid. Fixed tissues were processed and sections of 3-5 micron thickness were made and sections were stained with Ehrlich’s haematoxylin-Eosin solution. Age dependent changes were noticed in the shape and diameter of lymphoid follicle, thickness of cortex, diameter of medulla and height of the surface epithelium. Dendritic cells noticed in the follicles increased with advancement of age. During involution, reduction in lymphocyte population, fatty changes and epithelial cysts were noticed in both the sexes.
Bursa of Fabricius a lymphoepithelial organ peculiar to birds originated from the proctodeal wall of the cloaca and is placed dorsal to the cloaca. The avian bursa cloacalis Fabricii is responsible for the development and differentiation of B lymphocytes (Glick and Olah, 1993). In addition to its central role in B-lymphocyte maturation, the bursa of Fabricius also functions as a peripheral immunological organ associated with intestine. The present study was proposed to give a clear picture on age dependant changes and also involutory changes in bursa of Fabricius of guinea fowl.
Materials and Methods
The bursa of Fabricius was collected from apparently healthy guinea fowls (pearl variety) of different age groups ranging from day-old to six months of age at monthly interval. Each group consisted of six birds (three males and three females). Tissues of bursa of Fabricius were fixed in 10 per cent neutral buffered formalin and Bouin’s fluid. Fixed tissues were processed through ascending grades of alcohol, cleared in xylene and embedded in paraffin wax at 58-60oC. Sections of 3-5 micron thickness were stained with Ehrlich’s haematoxylin-Eosin (Bancroft et al.,2013). The age related and involutory changes in the bursa of Fabricius were recorded and the collected data were analysed as per the procedures of Snedecor and Cochran (1992).
Results and Discussion
Age Related Histological Changes
Histologically, the bursa of Fabricius presented inner tunica mucosa, middle tunica muscularis with inner circular and outer longitudinal smooth muscle fibres and outer tunica serosa. Tunica mucosa was thrown into longitudinal folds (plica) lined by surface epithelium. These mucosal folds were filled with lymphoid follicles and individual follicles were separated from each other by connective tissue septa (Basha, 1993). The surface epithelium was of pseudostratified columnar type over the lymphoid follicles and stratified cuboidal type in the rest of the regions which were not directly associated with the lymphoid follicle. The lymphoid follicle was divided into cortex and medulla; both being filled with lymphocytes and dendritic cells as stated by Jayachitra (2008).
The height of surface epithelium (Table 1) reached a maximum of 37.49 ± 2.02 µm in males and 45.83 ± 1.42 µm in females for pseudostratified columnar epithelium and 19.66± 7.15 µm in males and 24.17 ± 3.26 µm in females for stratified cuboidal epithelium at the age of 4 months. This differed from the findings of Hashimoto and Sugimura (1976) in ducks that after the sharp increase in height of epithelium observed at 5-7 weeks of age, the increase reappeared only at 13 weeks of age with a steady decrease at 22 weeks of age. Length and width of the primary plica were 1739.67±11.94 µm and 897.31± 7.01 µm in males and 2094.21± 13.82 µm and 1328.05 ± 8.87 µm in females at 4th month of age. The respective values for the secondary plica were 1282.06 ± 9.92 µm and 511.35 ± 8.02µ m in males and 1435.91 ± 10.04 µm and 864.32 9.08 µm in females at 4th month of age (Table 2). There after the length and width of both the plicae decreased as the age advanced. The lymphoid follicle was rounded in shape upto one month of age and became irregular as the age advanced. This finding also disagreed with those of Olah and Glick (1978) who stated that the shape of the follicle was like a bottle with spherical belly and cylindrical neck. The change in shape may be attributed to species variations.
Table 1: Histometry of the lymphoid follicle and surface epithelium of bursa of Fabricius in different age groups between sexes in Guinea fowl
|Diameter of lymphoid follicle ( µm)||Thickness of cortex (µm)||Diameter of medulla (µm)||Height of surface epithelium (µm)|
|Age groups||Sex||Pseudo stratified columnar (µm)||Stratified cuboidal (µm)|
|1st month||Male||209.83 ± 8.32||37.11 ± 4.98||113.78 ± 5.22||25.49 ± 2.78||12.09 ± 5.24|
|Female||159.06 ± 5.64||31.47 ± 5.13||103.22 ± 4.15||27.21 ± 6.24||15.24 ± 1.56|
|2nd month||Male||249.48 ± 9.07||41.56 ± 2.77||134.92 ± 1.19||28.13 ± 2.62||14.24 ± 2.72|
|Female||189.55 ± 6.64||33.98 ± 4.19||119.02 ± 2.24||30.16 ± 8.14||17.81 ± 6.25|
|3rd month||Male||271.23 ± 11.87||43.78 ± 2.52||157.08 ± 5.26||30.76 ± 1.62||16.07 ± 2.24|
|Female||291.39 ± 2.55||39.81 ± 5.16||151.81 ± 6.33||36.33 ± 6.18||19.77 ± 1.51|
|4th month||Male||378.91 ± 10.04||49.35 ± 2.26||195.34 ± 4.18||37.49 ± 2.02||19.66 ± 7.15|
|Female||265.61 ± 9.11||37.33 ± 5.25||134.29 ± 3.36||45.83 ± 1.42||24.17 ± 3.26|
|5th month||Male||327. 13 ±12.72||42.73 ± 3.67||162.41 ± 6.19||22.15 ± 6.24||12.93 ± 3.13|
|Female||233.68 ± 11.09||34.21 ± 2.45||129.11 ± 4.21||32.06 ± 4.16||10.29 ± 1.92|
The respective diameter of the lymphoid follicle, thickness of cortex and diameter of medulla increased gradually from day-old and reached its highest mean of 378.91± 10.04 µm, 49.35 ±2.26 µm and 195.34 ± 4.18 µm at the age of 4th month in males and 291.39± 2.55 µm, 39.81± 5.16 µm and 151.81± 6.33 µm at the age of 3rd month in females (Table 1). These present results contradicted with those of Basha (1993) who observed that in Japanese quail, the size of the follicles increased upto 58 days of age and thereafter gradually decreased upto 145 days of age. The diameter of the lymphoid follicles, cortex and medulla was greater in males than in females. As revealed by Ciriaco et al. (1994) in pigeon, the numbers of dendritic cells increased with advancement of age. For the first two months of life, the mast cells and plasma cells were more in bursa of Fabricius of both the sexes. But in contrary, Karaca et al. (2006) stated that the mast cells increased in number only upto 0-7 days of post hatch in chicken. Hashimoto and Sugimura (1976) also reported that the plasma cells increased markedly from the day of hatching to 3 weeks of post hatch life in White Pekin ducks. Hence it is assumed that the lymphocytic population probably depleted from the 2nd month onwards, leading to a concomitant decrease in the conversion of lymphocytes to plasma cells.
Table 2: Histometry of the plicae of bursa of Fabricius in different age groups between sexes in Guinea fowl
|Length of plicae||Width of plicae|
|1st month||Male||1395.07 ± 7.24||844.64 ± 6.24||480.64 ± 5.80||306.73 ± 8.63|
|Female||1452.74 ± 6.92||912.27 ± 5.11||685.44 ± 4.86||493.21 ± 5.46|
|2nd month||Male||1567.94 ± 8.89||976.46 ± 8.32||598.88 ± 9.79||353.05 ± 3.49|
|Female||1779.08 ± 7.12||1154.83 ± 5.64||847.21 ± 5.35||591.68 ± 3.84|
|3rd month||Male||1638.24 ± 9.03||1103.93 ± 7.25||664.02 ± 4.13||474.43 ± 6.77|
|Female||1987.59 ± 8.43||1337.29 ± 8.93||1194.74 ± 8.59||738.44 ± 6.12|
|4th month||Male||1739.67 ± 11.94||1282.06 ± 9.92||897.31 ± 7.01||511.35 ± 8.02|
|Female||2094.21 ± 13.82||1435.91 ± 10.04||1328.05 ± 8.87||864.32 ± 9.08|
|5th month||Male||1223.49 ± 14.68||994.76 ± 12.48||719.44 ± 9.43||468.36 ± 9.04|
|Female||1302.28 ± 12.26||1016.35 ± 7.25||1038.39 ± 5.24||775.44 ± 8.79|
Age Related Involutory Changes
The involutory changes started at the age of two months in both the sexes. But Milicevic et al. (1986) observed an advanced rate of involution in males with only the initial sign of bursal involution in females at 6 months of age in chicken. In both the sexes, depletion of lymphocytic population from periphery of the cortex, medulla and separation of cortex from adjacent follicles were noticed at the beginning of involution as observed by Firth (1977) in chicken. As age advanced, severe depletion of lymphocytes from cortex and medulla, with vacuolations in the medulla were noticed. Severe fatty changes in the subepithelial and interfollicular connective tissue and formation of epithelial cysts were seen as mentioned by Saifuddin et al. (1988) in Shaver cockerels.
In later stages of involution, the height of the surface epithelium was reduced, with only vacuolated structures being visible in the areas of epithelium. This is in accordance with the findings of Bickford et al. (1985) in White Leghorns. Size of follicles decreased and the amount of collagen fibres and reticular fibres increased in the subepithelial and interfollicular connective tissue as reported by Hashimoto and Sugimura (1976) in ducks.
The shape and diameter of lymphoid follicle, thickness of cortex, diameter of medulla and height of the surface epithelium underwent age dependent changes. Dendritic cells noticed in the follicles increased with advancement of age. In both the sexes, the involutory changes similar. The changes included depletion of lymphocytes, vacuolations with fatty changes in the interfollicular connective tissue and formation of epithelial cysts. The amount of connective tissue, particularly collagen fibres increased as age advanced.
The authors are thankful for the support of Tamil Nadu Veterinary and Animal Sciences University, Chennai, Tamilnadu-600051, India.