Interleukin‐7 expression during mouse thymus development

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Abstract
We have monitored the expression of interleukin‐7 (IL‐7) in the developing embryonic mouse thymus by a combination of quantitative polymerase chain reaction (PCR) and immunofluorescence microscopy. A strong specific signal for IL‐7 mRNA was detected by day 12 in the developing fetal thymus. IL‐7 mRNA was found to be maximally expressed on day 15, and then decreased over the next 5 days. Immunofluorescence staining of fetal thymus sections using an anti‐IL‐7 antibody confirmed these PCR data. IL‐7 protein expression was first detected at day 13 of development. At 14 days the intensity of the staining increased by a factor of three and stayed at this level over the next 4 days. The same anti‐IL‐7 antibody used for immunofluorescence, blocked the proliferation of fetal thymocytes in organotypic cultures. In addition, we detected mRNA coding for IL‐2 and SCF (also known as the steel factor or KL) in embryonic thymocytes. The implications of these findings for early thymocyte growth are discussed.