Expression of HIV Tat mRNA and protein in tissues of transgenic mice. (A) Northern blot analysis Tat mRNA in two independent transgenic lines, 21 and 29. Whole-cell RNA was extracted from spleen, thymus, and other tissues. The RNA samples (20 μg per lane) were size-separated, blotted onto a membrane, and incubated with radiolabeled Tat cDNA probe and, subsequently, with a β-actin cDNA probe. The blot was washed and exposed to x-ray film. (B) Expression of Tat mRNA in lymphoid cells. Lymphocytes were sorted into T-cell and B-cell components, from which total RNA was prepared, size separated, and blotted. A mouse GAPDH cDNA probe was used as an internal control. Sp, spleen; Th, thymus; CD4, CD4-positive T cell; CD8, CD8-positive T cell; B, B cell; M, monocyte. (C) Immunodetection of Tat in histologic sections of transgenic spleens. Spleens of Tat transgenic animals and littermate controls were processed for histology, sectioned, and the sections incubated with an anti-Tat monoclonal antibody. The specificity of this antibody for Tat was documented previously.33 The secondary antibody was a horseradish peroxidase-streptavidin conjugate (×25).