A new human monoclonal plasma cell line, designated UTMC-2, was establ
ished from the pleural effusion of a patient with immunoglobulin (Ig)A
kappa-related multiple myeloma. The cultured cells were Epstein-Barr
virus-negative and exhibited the morphological and ultrastructural fea
tures characteristic of plasma cells. Immunohistochemical analyses rev
ealed the presence of cytoplasmic IgA kappa as well as the plasma cell
-associated surface antigens CD38 and GD56. Other B-cell markers, incl
uding CD10, CD19, CD2O, and HLA-DR, were absent. The UTMC-2 cells were
interleukin (IL)-6 responsive: Co-culture with IL-6 increased IgA kap
pa synthesis and cell proliferation in a dose-dependent manner. In con
trast, an IL-6 antisense oligonucleotide had an opposite effect. Altho
ugh the expressed IL-6 mRNA (as demonstrated by scriptase-polymerase c
hain reaction (RT-PCR)) and contained IL-6, the concentration of this
cytokine in cell culture supernatants was less than that detectable by
the enzyme-linked immunosorbent assay (ELISA) employed (i.e. <3 pg/ml
). Further, cell growth was not inhibited by polyclonal or monoclonal
anti-IL-6 antibodies. Flow cytometric analysis revealed that IL-6 rece
ptors present on the surface of the UTMC-2 cells were not saturated wi
th endogenous IL-6. Taken together, these results indicate that, in th
is human plasma cell line, IL-6 functions uniquely in an intracellular
autocrine fashion to enhance Ig synthesis and cell growth. In this re
spect, the UTMC-2 cells represent a novel resource for further study o
f the role of IL-6 in the pathogenesis of multiple myeloma.