Resistance to Moloney Murine Sarcoma Virus (M-MuSV) Tumor Induction is Associated with Natural Antibody Production to «Endogenous» Moloney Leukemia Virus (M-MuLV) in Balb/Mo Mice

Role of Infectious Virus Expression and Immune Response in Retrovirus-Induced Oncogenesis

Some of the parameters involved in retrovirus-induced oncogenesis were analyzed in newborn mice injected with Moloney-murine leukemia virus (M-MuLV) as well as in adults who received the virus by the intraperitoneal (i.p.) or intrathymic (i.t.) route. The neonatally injected mice were permissive for both viral replication and virus-induced cell-surface antigen expression on thymus cells, peripheral T and B lymphocytes, and macrophages, whereas the M-MuLV was not present in the adult i.p. injected mice. Instead, in i.t. injected mice, the virus was expressed in thymus and peripheral T cells only, but was not detected in tail extracts as assessed by means of the UV-XC plaque assay. Lack of virus spread in adult-treated animals correlated with a prompt humoral and cellular immune response, whereas the highly viremic newborn inoculated mice showed negligible virus-specific antibody production and an extremely low frequency of splenic cytotoxic T lymphocyte precursors. Moreover, immune response in both groups of adult-treated mice efficiently prevented tumor induction by Moloney-murine sarcoma virus (M-MuSV), which has the same antigenic determinants as M-MuLV, its natural helper. In contrast, M-MuSV sarcomas grew progressively in newborn inoculated mice and killed the host. Finally, 80 % of neonatally injected mice developed lymphomas, whereas all treated adults remained free of disease for more than 15 months. These findings imply that the immune response may, in fact, prevent retrovirus-induced oncogenesis through restriction of virus replication and/or destruction of virus-infected cells.

Are natural antibodies involved in tumour defence?

Natural antibodies (NAb) are found in the serum of healthy individuals. These antibodies are produced without any apparent specific antigenic stimulation. They are one part of the circulating immunoglobulins and are found in virtually all vertebrate species. NAb react to various self- and non-self antigens. A protective function in different infection models could be demonstrated. Several groups have reported the ability of NAb to bind to tumour cells. Their possible role in tumour defence is documented in mice. The present status of attempts to characterise the role of NAb in tumour defence is discussed, particularly as regards the human immune system. This paper focuses on antibody cell interactions and discusses the genetic background of the Nab-producing B-cells.

Tolerance to viral antigens in Mov-13 mice carrying endogenized Moloney-murine leukemia virus

In virus-positive (V+) C57BL/6 Mov-13 mice, Moloney-murine leukemia virus (M-MuLV) is integrated into the germ line and expressed early in lymphoid and nonlymphoid organs. The pattern of immune reactivity to viral antigens in these mice was studied and compared to that of their virus-negative (V-) counterparts. Using a radioimmuno-binding or -precipitation assay, V- mice showed good antibody production after challenge with Moloney-murine sarcoma virus (M-MSV), but no antibodies were detected in V+ mice. Moreover, Mov-13 V+ mice failed to generate virus-specific cytotoxic T lymphocytes (CTL) in secondary mixed-leukocyte tumor cell culture (MLTC) while V- mice showed a strong cytotoxic response. This lack of activity in mass V+ cultures was due to a very low frequency of CTL precursors which did not increase following in vivo challenge with M-MSV or in vitro stimulation with MBL-2 Moloney leukemia cell line. These findings indicate that early M-MuLV activation in Mov-13 V+ mice induces a state of tolerance to viral antigens involving both the humoral and cellular immune responses and related to the high incidence of T-cell lymphomas.