Immunolocalization of serum proteins in xenografted mouse model of human tumor cells by various cryotechniques.

The transport mechanism of soluble molecules throughout the interstitial matrix is closely associated with human tumor behavior in vivo. However, the examination of soluble components in histological architectures has been hampered by artifacts caused during conventional tissue preparation. In this study, the immunodistribution of intrinsic and extrinsic serum components in tumor tissues was examined in xenografted human tumor cells using 'in vivo cryotechnique' (IVCT) and cryobiopsy, where target tissues are directly cryofixed in vivo. Human lung cancer cells were subcutaneously injected into the dorsal flank of nude mice, and paraffin sections and cryosections of produced tumors were prepared with different methods. Immunolocalization of serum proteins, including albumin, immunoglobulin G (IgG) and IgM, as well as intravenously injected bovine serum albumin (BSA) was examined. Their immunodistribution was more clearly observed in the interstitium by both IVCT and cryobiopsy than conventional methods. IgM was immunolocalized within blood vessels, whereas albumin and IgG were observed in the tumor interstitium. Moreover, intravenously injected bovine serum albumin exhibited leakage from the blood capillaries into surrounding connective tissues in 24 h, but it gradually diffused to the interstitium of the tumor masses during 3 days. These results suggest that molecular leakage from blood capillaries varies significantly in different areas of developing tumors, and that small serum proteins, but not large ones, were abundantly immunolocalized in the tumor interstitium. Both IVCT and cryobiopsy were found to be useful for immunohistochemical studies of soluble molecules in tumors with blood circulation, and may therefore be helpful for further histopathological analyses.