Postnatal Development of Bronchus-Associated Lymphoid Tissue (Balt) in the Rat, Rattus Norvegicus

Abstract

SummaryThe pattern of development of bronchus-associated lymphoid tissue (HALT) in specified-pathogen-free and conventional (non-barrier maintained) rats over the initial 4 weeks of life appeared to be similar. HALT first appeared around the 2nd week of life and increased in amount over the following 2 weeks. Overlying large nodules of HALT the bronchial epithelium becomes infiltrated by lymphocytes to form a Iymphoepithelium.This transformation occurs earlier in conventional rats, possibly because of the differing antigen levels to which they are exposed.The morphology of bronchus-associated lymphoid tissue (BALT) in the rat and rabbit has been described in some detail by Beinenstock, Johnston & Perey (1973a) and by Chamberlain, Nopajaroonsri & Simon (1973). Occasional studies during the past century or so have referred to BAL T -notably that of Klein (1875) and more recently Macklin (1955) and Brundelet (1965). Despite these few studies, little is known of BAL T other than its structural characteristics.BAL T is found in the rat lung, often in association with the major bronchi and lying just beneath the bronchial epithelium, which it often infiltrates to form an overlying lymphoepithelium.It had been assumed for many years that, because the amount of lymphoid tissue in the lung is markedly increased in cases of chronic respiratory disease (CRD}--typically in cases of mycoplasma and Pasteurella pneumotropica infection (Lindsey, Baker, Overcash, Cassell & Hunt,1971}-that BALT was present as a manifestation of a local immune response to infection. It was thus thought that in 'clean' or germ-free animals BALT would be minimal or absent. However, it has recently become clear that BALT is consistently present in rats reared under germ-free conditions (Bienenstock et al., 1973a;Lamb, 1975) The present study was carried out with the object of determining at what stage BALT developed in the lungs of neonatal rats, both 'conventionally' and barrier maintained, and to relate this to the development of antibody production within the lungs of those rats. Materials and methods AnimalsCFY strain (Sprague-Dawley derived) rats were obtained from Anglia Laboratory Animals (Alconbury, Huntingdon, PE18 6ES, UK). In the first part of the study 10 adult female rats were mated and the occurrence of vaginal plugs noted in order that subsequent foetal development could be accurately dated. These rats were brought outside barriered conditions and their litters were raised in a 'conventional' laboratory environment. The resultant litters were killed, in batches of 7 rats, at ages 1,3,6,9, 14,21,28 and 42 days. 5 adult (6 month old) rats raised under the same conditions were also killed.In the 2nd part of the study, specified-pathogen-free (SPF) animals were used. These had been reared entirely under barrier conditions. A group of rats of 1, 3, 7, 14, 28 and 56 days, and an adult group of 6 months, of age were also examined. 7 animals were killed at each age investigated. Preparation of tissuesEach group of 7 rats was killed by an int...

Inducible Bronchus-Associated Lymphoid Tissue: Taming Inflammation in the Lung

“…Once that developmental window is passed, lymph nodes are no longer able to develop, even if all the necessary cells and molecules are present ( 8 ). In contrast, the development of iBALT requires an inflammatory or infectious stimulus in most species ( 25 , 26 , 70 – 73 ), including rats ( 74 – 77 ), mice ( 78 ), goats ( 79 ), chicken ( 33 ), and humans ( 29 , 73 , 80 ), and its development can be initiated throughout life. In contrast, pigs are reported to form iBALT in the lungs during fetal development ( 81 ).…”

MALT structure and function in farm animals

“…Both organized lymphoid nodules with primary and secondary lymphoid follicles and unorganized aggregates of lymphocytes can be seen. They may be different developmental stages of the same structures [6,35].…”

Lymphoid organogenesis in brief

“…In contrast to the LN and PP, which develop prenatally, the formation of NALT, BALT and the intestinal isolated lymphoid follicles (ILF) and cryptopatches (CP) as part of the GALT, was recently shown to occur postnatally in mice and rats (reviewed in [63][64][65]). For NALT development, the molecular requirements seem to differ from those identified for the formation of LN and PP: Both LTbR triggering, as well RORc were shown to be indispensable for NALT formation [66,28].…”