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Development of bronchus associated lymphoid tissue (BALT) in the rat, with special reference to T- and B-cells
The development of bronchus associated lymphoid tissue was studied in normal rats, in serial sections, using both routine histological techniques and the two-step immuno-peroxidase method on cryostat sections for demonstration of T lymphocytes, IgM-, IgG- and IgA-bearing B lymphocytes and plasma cells, respectively. BALT first appears 4 days postpartum (p.p.) as a condensation of reticulum cells near a lymph vessel, between the main bronchus and the accompanying artery. Only a few lymphocytes are present at first. Vascularisation is considerable 8 days p.p. and includes high endothelial venules. Leucocytes are seen in transit in both blood- and lymph vessel walls. Lymphocytes populate the area under the epithelium from about 2 weeks p.p. A few IgM, IgG- and IgA-bearing B cells are already present at 4 days, and rapidly increase in numbers; T cells usually appear at day 8. Discrete T- and B-cell areas do not appear until 4 weeks and are only observed regularly after 12 weeks, when secondary follicles appear. BALT starts development at a similar time to other peripheral lymphoid organs but apparently achieves immunological activity later. It is concluded that antigens probably play an important part in organising BALT.
The development of bronchus associated lymphoid tissue was studied in normal rats, in serial sections, using both routine histological techniques and the two-step immuno-peroxidase method on cryostat sections for demonstration of T lymphocytes, IgM-, IgG- and IgA-bearing B lymphocytes and plasma cells, respectively. BALT first appears 4 days postpartum (p.p.) as a condensation of reticulum cells near a lymph vessel, between the main bronchus and the accompanying artery. Only a few lymphocytes are present at first. Vascularisation is considerable 8 days p.p. and includes high endothelial venules. Leucocytes are seen in transit in both blood- and lymph vessel walls. Lymphocytes populate the area under the epithelium from about 2 weeks p.p. A few IgM, IgG- and IgA-bearing B cells are already present at 4 days, and rapidly increase in numbers; T cells usually appear at day 8. Discrete T- and B-cell areas do not appear until 4 weeks and are only observed regularly after 12 weeks, when secondary follicles appear. BALT starts development at a similar time to other peripheral lymphoid organs but apparently achieves immunological activity later. It is concluded that antigens probably play an important part in organising BALT.