Immunology Letters 74 (2000) 133 – 139
Splenic cytotoxic cells recognize surface HSP70 on culture-adapted
EL-4 mouse lymphoma cells
Eugene D. Ponomarev, Tatyana N. Tarasenko, Alexander M. Sapozhnikov *
Diision of Immunology, Shemyakin and Ochinniko Institute of Bioorganic Chemistry, 16 /10 Miklukho -Maklaya Str.,
117871 Moscow V-437, Russia
Received 7 May 2000; received in revised form 13 June 2000; accepted 13 June 2000
Abstract
Heat shock proteins (HSPs) are intracellular proteins which function as molecular chaperones. At the same time, translocation
of HSPs to the cell surface has been observed in stressed, infected and transformed cells. It seems plausible that surface HSPs may
represent molecular targets for recognition and elimination of ‘altered’ cells by cytotoxic lymphocytes. Previously we demonstrated
that EL-4 mouse lymphoma cells growing in vitro express HSPs on their plasma membrane. In this study, we tested the hypothesis
that surface HSPs present on EL-4 cells may mediate their recognition and killing by cytotoxic lymphocytes. We have found that
susceptibility of culture-adapted EL-4 cells to in vitro lysis by syngeneic and allogeneic splenocytes correlated with the expression
of HSP70 on EL-4 cells. Moreover, cytotoxicity was blocked by pretreatment of EL-4 target cells with anti-HSP70 antibody,
whereas antibodies to MHC class I molecules and Thy1 did not have such effect. Cytotoxicity against EL-4 lymphoma was not
MHC class I-restricted, and was not decreased after depletion of CD8
+
cells from the effector cell population. We conclude that
in vitro killing of EL-4 cells is mediated, at least in part, by NK cells via recognition of HSPs present on the surface of tumor
cells. Thus, cytotoxic response against EL-4 lymphoma should serve as a good model to study the role of HSPs in anti-tumor
immunity. © 2000 Elsevier Science B.V. All rights reserved.
Keywords: Heat shock proteins; NK cells; EL-4; Cytotoxicity; Mouse; H-2
b
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1. Introduction
Heat shock proteins (HSPs) are highly conserved and
ubiquitously expressed proteins that are predominantly
located in the cytoplasm and function as molecular
chaperons [1]. However, evidence has now accumulated
that translocation of HSPs to the cell surface may occur
in stressed, infected and transformed cells [2 – 4]. Al-
though mechanisms of translocation remain unclear, it
seems plausible that surface HSPs may play a role as
molecular markers of ‘altered’ cells, destined to be
eliminated by cytotoxic lymphocytes [3,4]. Some tumors
produce large amounts of HSPs that are expressed on
the cell surface and can potentially attract NK cells
[5,6]. Surface expression of HSP72, an inducible form
of HSP70, on human lung carcinoma cells was associ-
ated with their increased sensitivity to lysis by NK cells
[7]. Also, IL-2 activated human NK cells were shown to
recognize HSP72 on the surface of K562 ery-
throleukemia and human sarcoma cells subjected to
heat shock [8–10]. It should be noted, however, that
hyperthermia does not always increase tumor cell sus-
ceptibility to killing. Thus, heat shock did not lead to
enhanced killing of human melanoma cells, even
though it resulted in the induction of surface HSP70,
and simultaneous down-regulation of HLA expression
on the tumor cells [11]. Mechanisms by which surface
HSPs may mediate recognition and elimination of tu-
mor by cytotoxic lymphocytes remain poorly under-
stood. One possibility is that immunogenic peptides
expressed in association with HSP70 and HSP90 on
tumor cells can be recognized by T lymphocytes, as well
as NK cells [8,12]. Another possibility is that HSP
itself, e.g. HSP60 and HSP70 (grp75) on the surface of
tumor cells can be recognized by T cells in a
non-MHC restricted manner [13].
* Corresponding author. Tel.: +7-95-3304011; fax: +7-95-
3357103.
E-mail address: amsap@ibch.siobc.ras.ru (A.M. Sapozhnikov).
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