Immunocytochemical localization of latent transforming growth factor-beta 1 activation by stimulated macrophages

Transforming growth factor-beta 1 (TGF-beta) is secreted in a latent form c onsisting of mature TGF-beta noncovalently associated with its amino-termin al propeptide, which is called latency associated peptide (LAP). Biological activity depends upon the release of TGF-beta from the latent complex foll owing extracellular activation, which appears to be the key regulatory mech anism controlling TGF-beta action. We have identified two events associated with latent TGF-beta (LTGF-beta) activation in vivo: increased immunoreact ivity of certain antibodies that specifically detect TGF-beta concomitant w ith decreased immunoreactivity of antibodies to LAP. Macrophages stimulated in vitro with interferon-gamma and lipopolysaccharide reportedly activate LTGF-beta via cell membrane-bound protease activity. We show through dual i mmunostaining of paraformaldehyde-fixed macrophages that such physiological TGF-beta activation is accompanied by a loss of LAP immunoreactivity with concomitant revelation of TGF-beta epitopes. The induction of TGF-beta immu noreactivity colocalized with immunoreactive betaglycan/RIII in activated m acrophages, suggesting that LTGF-beta activation occurs on the cell surface . Confocal microscopy of metabolically active macrophages incubated with an tibodies to TGF-beta and betaglycan/RIII prior to fixation supported the lo calization of activation to the cell surface. The ability to specifically d etect and localize LTGF-beta activation provides an important tool for stud ies of its regulation. J. Cell. Physiol. 178:275-283, 1999. (C) 1999 Wiley- Liss, Inc.