H. Katano et al., Expression of human herpesvirus 8 (HHV-8)-encoded immediate early protein,open reading frame 50, in HHV-8-associated diseases, J HUMAN VIR, 4(2), 2001, pp. 96-102
Objectives: To investigate the expression of the open reading frame (ORF) 5
0 protein, a human herpesvirus 8 (HHV-8)encoded immediate early protein, in
HHV-8-associated diseases.
Study Design/Methods: We developed a rabbit anti-ORF50 protein polyclonal a
ntibody, and investigated the ORF50 protein expression by immunohistochemis
try using primary effusion lymphoma (PEL) cell lines and tissue sections of
Kaposi's sarcoma (KS), HHV-8-associated solid lymphoma, and multicentric C
astleman's disease (MCD).
Results: Western blot analysis revealed that this antibody reacted with a 1
10-kd protein in the lysate of phorbolester-stimulated HHV-8-infected PEL c
ell lines. Immunohistochemistry revealed that a very small population of ce
lls expressed the ORF50 protein in KS and HHV-8-associated solid lymphoma c
ells, and almost all these cells expressed HHV-8-encoded latency-associated
nuclear antigen. The ORF50 protein expression was also rare in the cells o
f PEL cell lines, and the staining pattern was diffuse or dot-like in the n
uclei, overlapping partially with that of promyelocytic leukemia protein. I
n MCD, however, the ORF50 protein was expressed in some cells of the mantle
zone of the lymphoid follicle.
Conclusions: The ORF50 protein expression in vivo was considerably rare in
KS, HHV-8-associated solid lymphoma, and PEL, but was more frequent in MCD.
Rare expression of this transactivator protein in HHV-8-associated maligna
ncies causes low expression levels of other lytic proteins and may play a r
ole in the maintenance of the latent infection. This is the first report de
scribing the expression of an immediate early protein of HHV-8 in cases of
HHV-8-associated diseases.