Figure 3

Lymphocytes in human BALT. (A-D): Semi-serial frozen sections of BALT were stained with mAbs against CD19 and CD3 (A), CD4 and CD8 (B), CD4 and CD45RO (C), and CD4 and CD45RA (D). L is in the airway lumen of the bronchus. (A) B cell follicle (CD19⁺, red) surrounded by T cells (CD3⁺, green). (B) CD4⁺ cells (red) outnumber CD8⁺ cells (green). (C) Almost all BALT CD4⁺ cells have a memory phenotype (CD4⁺CD45RO⁺; yellow). (D) CD4⁺ cells with a naive phenotype (CD4⁺CD45RA⁺, yellow) are very rare in BALT. Most cells in the B cell follicle are CD4^-CD45RA⁺ (green). (E-H): Semi-serial frozen sections of BALT from a different patient were stained with FITC-anti-CD3 mAb combined with a PE-conjugated mAb against an adhesion molecule or a negative control antigen. L is in the airway lumen of the bronchus. Most BALT T cells, as defined by expression of CD3, also expressed LFA-1 (E, yellow); a minority of BALT T cells expressed α₄ integrin (F, yellow) or L-selectin (G, yellow). In contrast, most BALT B cells (CD3^-) express LFA-1 (E, red), α₄ integrin (F, red) and L-selectin (G, red). The PE-negative control mAb did not stain T or B cells in BALT (H). (two-color immunofluorescence stains. original magnification 200×).