Studies On The Structure And Function Of The Aggregated Lymphoid Nodule Area In The Abomasum Of Bactrian Camels (Camelus Bactrianus) Of Different Ages

The aggregated lymphoid nodule area(ALNA) in the third compartment of the stomach of Chinese Alashan Bactrian camels is a recently(2003) described species-specific anatomical structure by Wang Wen-hui.To further investigate the immunological morphological characteristics and function of it,and establish the relationship between this structure and animal age,normal Bactrian camels were firstly studied using the technologies of anatomy, histology,histochemistry and electron microscopy while the age groups were defined as follows:young camels(0.5-2 years old),pubertal camels(3-5 years old),middle-aged camels (6-16 years old) and old camels(17-20 years old).The exact anatomical location,and the anatomical,microstuctural and ultrastructural characteristics of the mucosa of the ALNA were described in detail as was the relationship between this structure andanimal age.On the above basis,Bactrian camel models were imitated using Bacillus subtilis as an oral tracer antigen,then the function and immune mechanisms of the ALNA were discussed after detecting relevant indicators.In addition,the changes of morphological characteristics of the ALNA and its development time during the ontogenic courses were also studied.The results showed that:(1) The ALNA of the Bactrian camels not only has a particular anatomical location and distinct mucosal structure,but also changes with age.The ALNA extended along the ventral wall of the isthmus,from the origin of the proximal enlargement and along the curvatura ventriculi minor.The mucosal folds of the ALNA were much thicker than and were clearly demarcated from those of adjacent non-ALNA.Based on the morphology of the mucosal folds,the ALNA could be divided into reticular and longitudinal regions.On statistical analysis,the ALNA was found to enlarge prior to puberty,peak in size at puberty, and then regress.A small remnant ALNA was found in 20-year-old camels,although the germinal centres of the contained lymphoid nodules were not as obvious at this time.(2) In addition to some similarities to gut-associated lymphoid tissues,the ALNA also has its special histological characteristics which may change with ageing.The mucosal folds on the ALAN of the young and pubertal camels are higher and wider than those of older animals,and most lymphoid nodules are round,oval,and cuneiform shaped aggregating in the submucosa continuously although some nodules are arranged in two or more rows,especially at the top of wide mucosal folds.All the lymphoid nodules are with distinct germinal centers,and are distributed evenly on both sides of the axis of the mucosal folds.The number of the follicular associated epithelium(FAE) and lymphoid nodules in the mucosal folds are very abundant as well as the number of reticular fibers and plasma cells.On the contrary,the mucosal folds on the ALNA of the middle-aged and old camels become lower and thinner than those of the young animals.Most lymphoid tissues of this age are diffuse lymphoid tissues while lymphoid nodules are oval and irregular shapes,and are arranged interruptedly on both sides of the mucosal fold axis unevenly,which are generally more on one side,fewer on the other side,or even absent.Furthermore,the germinal centers are still obvious while the number of the lymphoid nodules in the mucosal folds as well as the number of reticular fibers and plasma cells decrease gradually.These results are consistent with the anatomical findings,and can further confirm and explain the regularity and immunological significance of structural characteristics changes with ageing of the ALNA.(3) The ultrastructural studies suggested that the ALAN has its unique ultrastructural characteristics compared to the non-ALNA of stomach,and the ultrastructural characteristics are different between age groups.The cardiac glands in the ALNA of young Bactrian camels have more gland cells with small opening diameter,and the numbers of antigen uptake sites -FAE on the mucosal surface are very abundant as is the mucus.Whereas the cardiac glands in the ALNA of the old camels have wider opening and fewer gland ceils while the quantity of FAE and mucus on the mucosal surface also becomes fewer.Therefore,both the mechanical barrier and mucosal immune barrier of the ALNA regress with increasing age in Bactrian camels.(4) Observations on animal models showed that:while many Bacillus subtilis adhere to the mucosal surface of the FAE,there are a fewer on the non-FAE and non-ALNA in the experimental group,and there is none anywhere of the control group.In addition,there are a few Bacillus subtilisis penetrating the epithelium into the laminae propria of the FAE in the experimental group. Moreover,the numbers of immune-related cells,such as intraepithelial lymphocytes,plasma cells,mast cells and argyrophilic cells have all significant proliferated in the experimental group.Ultrastructural studies indicated that after feeding bacteria,the mucus and M cells of the ALNA increase whlie the epithelial cells proliferate prominently,which leads to the surface structure of the ALNA changed from "honeycomb" into porous structure.(5) The results of the ontogenic morphology of the ALNA showed that the first primordial lymphoid nodules of the ALNA was encountered in the midterm of gestation whereas the lymphoid nodules development was observed to have been completed in the last one or two months of pregnancy.In addition,the initial development location of lymphoid nodules location was in the lamina propria,and partial lymphoid nodules penetrated the lamina muscularis into the submucosa.In conclusion,the ALNA of the Bactrian camels not only has special digestive structure, but also has special immune morphological structure.The changes of ALNA with ageing were related to the physiological atrophy,and is a useful evidence of immunesenescence and mucosal immunesenescence.A series of the immune celluar reactions and mucosal barrier changes of ALNA take place to defend the invasion of exogenous antigen,and the mucosal immune mechanism of the ALNA is similar to PP in the intestine while the FAE is the main antigen uptake sites.In addition,similar to the development characteristics of the ileal Peyer's patches that reported in bovine and sheep,the development of the ALNA has been completed in the gestation,and it regress after puberty,so it may be a primary immune organ.