Inducible heat shock protein 70 in rat cardiac allograft and its immunohistochemical localization in cardiac myocytes

Background, Heat shock proteins (HSP) are induced by a variety of stress and are presumed to play an important role in protecting cells from the effects of stress, Some evidence exists that HSP is involved in allograft rejection, Recently, an increase of inducible HSP 70 in heterotopic rat heart allografts was shown by quantitative Western blotting, To determine a possible mRNA induction and the localization of inducible HSP 70, we examined 19 heart transplants in rats, Methods, Fisher F344 rat hearts were heterotopically transplanted into Lewis recipients (n = 10), and nine cardiac isografts (Fisher to Fisher) were performed, The 19 native hearts of the recipients served as controls, Animals were killed on posttransplantation days 1, 3, and 5, The hearts were examined immunohistologically for inducible HSP and analyzed by a semiquantitative polymerase chain reaction for inducible mRNA, Results, The level of HSP 70 mRNA in the allograft increased from day 1 to 3 and day 3 to 5 after transplantation and was significantly higher than that of time-matched isografts (0.92 +/- 0.49 vs, 0.49 +/- 0.05 and 1.14 +/- 0.53 vs. 0.53 +/- 0.15; P < 0.05), The native hearts showed no elevated HSP 70 expression compared with isografts. Immunohistochemically, the majority of inducible HSP was located in cardiomyocytes adjacent to infiltrating lymphocytes, which where consistently negative. Conclusions, These results demonstrate that HSP mRNA expression in cardiac allografts is time-dependent, and its protein is expressed in cardiomyocytes.