Functional analysis of thymic B cells.
The expression of low- and high-affinity interleukin-5 receptors (IL-5Rs) on thymic B cells and reactivity of thymic B cells to IL-5 was investigated. Thymic B cells consist of two populations (CD5+ and CD5- B cells), as previously described. Three-color FACS analyses using anti-CD5, anti-IgK, and anti-IL-5R mAbs reveal that approximately 60% of both populations (CD5+ and CD5-) in the thymus possess IL-5R, detected by mAb H-7. In Scatchard plot analyses, IL-5Rs on thymic B cells are observed as low affinity receptors; the high-affinity IL-5R, which is known to be expressed on some IL-5-activated splenic B blasts or some IL-5-dependent cell line cells, is not clearly detected on thymic B cells. The reactivity of thymic B cells to IL-5 is found to be significantly lower than that of splenic B cells both in proliferative responses and LPS-induced IgM and IgA antibody responses. These findings are compatible with the expression of the low-affinity IL-5R on thymic B cells. The responsiveness of thymic B cells to either IL-6 or the combination of IL-4, IL-5 and IL-6 is also lower than that of splenic B cells. Furthermore, the thymic B cells are found to induce neonatal tolerance. Therefore, thymic B cells act as antigen-presenting cells in the negative selection of thymocytes, rather than as antibody-producing cells under the influence of foreign antigens and/or regulatory cytokines.
Fukuba
Y
Y
First Department of Pathology, Kansal Medical University, Osaka, Japan.
Inaba
M
M
Taketani
S
S
Hitoshi
Y
Y
Adachi
Y
Y
Tokunaga
R
R
Inaba
K
K
Takatsu
K
K
Ikehara
S
S
D000818:Animals; D000831:Animals, Newborn / Q000276:immunology; D001402:B-Lymphocytes / Q000166:cytology / Q000276:immunology*; D016207:Cytokines / Q000276:immunology; D005434:Flow Cytometry; D007108:Immune Tolerance / Q000276:immunology; D015848:Interleukin-5 / Q000276:immunology*; D008213:Lymphocyte Activation; D008285:Major Histocompatibility Complex / Q000276:immunology; D051379:Mice; D008807:Mice, Inbred BALB C; D008811:Mice, Inbred DBA; D018123:Receptors, Interleukin / Q000096:biosynthesis* / Q000276:immunology; D053649:Receptors, Interleukin-5; D013950:Thymus Gland / Q000166:cytology*
D016207:Cytokines; D015848:Interleukin-5; D018123:Receptors, Interleukin; D053649:Receptors, Interleukin-5