Lymphoid cells from many normal mice of a variety of inbred strains were found to have reactivity, in a 51Cr release cytotoxicity assay, against several syngeneic and allogeneic tumors. Very high reactivity was seen with effector cells from athymic nude mice, which was consistent with other evidence that the reactivity was not T-cell dependent. Target cells susceptible to lysis included tumors induced by oncogenic type-C viruses but also tumors induced by other means and expressing endogenous type-C viruses. The levels of natural reactivity were influenced by age, with highest cytotoxicity produced by cells from 5- to 8-week-old mice. Lymph-node cells, spleen cells, peritoneal exudate cells and peripheral blood lymphocytes all had cytotoxic reactivity. The specificity of the reactions was analyzed in detail by ana inhibition assay. Evidence was obtained for natural reactivty against several different antigens, each apparently associated with expression of murine endogenous type-C viruses.

Natural cytotoxic reactivity of mouse lymphoid cells against syngeneic and allogeneic tumors. I. Distribution of reactivity and specificity

Trans-membrane control of the receptors on normal and tumor cells. II. Surface changes associated with transformation and malignancy.

The levels of natural cell-mediated cytotoxicity against tumor cells in young BALB/c and BALB/c nude mice could be augmented by inoculation of a variety of mouse tumor cells or of mouse thymocytes. In older mice with low levels of spontaneous cytotoxic reactivity, inoculation of tumor cells led to rapid appearance of cytotoxicity. This augmented cytotoxicity reached a peak 3 days after inoculation, and then declined rapidly. The specificity of the augmented cytotoxicity appeared to be the same as that seen with natural cell-mediated cytotoxicity. The detected antigens were restricted to mouse tumor cells and thymocytes, and were absent on cells from other species. The effector cells after boosting also had the same cell surface characteristics as the natural cytotoxic effector cells, being non-adherent, non-phagocytic, and only weakly sensitive to treatment with anti-theta serum plus complement. In addition to this boosting by mouse tumor cells, marked increases in the levels of cytotoxicity were caused by a variety of murine viruses, including murine sarcoma virus and lymphocytic choriomeningitis virus. These effector cells also had the same properties as those seen with natural cytotoxic effector cells. The results indicate that the levels of natural cell-mediated cytotoxicity in conventional and athymic BALB/c mice can be consistently and rapidly boosted by inoculation with tumor cells or viruses. This should provide a valuable tool for better understanding of the mechanisms responsible for the expression of natural cytotoxicity and its relevance to in vivo resistance to tumor growth.

Augmentation of natural cytotoxic reactivity of mouse lymphoid cells against syngeneic and allogeneic target cells.

Publisher Summary This chapter discusses the multiple lymphocyte surface antigens of the mouse. A wide range of different antigens is described, ranging from those that have a broad tissue distribution to those highly restricted to specific lymphocytes and including others, such as viral-associated antigens. Special emphasis is placed on the Ly markers, in view of their extreme utility in defining functional subsets of lymphocytes. The new Qa antigens and the Ia system are also discussed. It describes genetic polymorphisms that lead to structural variations in the cell surface. These variations lead to differences between strains that subsequently elicit the production of antibody or graft rejection. The studies of cell membrane alloantigenic determinants (CMAD) have yielded generous rewards, particularly in the identification of the relationship between T-cell function and surface antigenic phenotype. The CMAD is used to distinguish among different functional subpopulations of lymphocytes. There are a number of examples where CMAD and murine leukemia virus are associated either directly or indirectly. Viral antibodies contaminating alloantisera are providing considerable problems in the analysis of CMAD.

Murine lymphocyte surface antigens.

The cell-type specificity of the toxin ricin, which ordinarily binds, enters, and kills cells through receptors containing galactose, has been altered by covalently binding it to a monoclonal antibody and by reversibly binding it to lactose. The antibody, a monoclonal rat IgG2b directed against the Thy 1.2 antigen, provides ricin with a new binding site for the murine thymus cell surface. Addition of lactose saturates the galactose-binding site on ricin and inhibits ricin from binding and killing cells via the galactose-containing receptors. The antibody-ricin hybrid protein, anti-Thy 1.2-ricin, formed with a thioether linkage, has been purified by size exclusion and affinity chromatography. When assayed by inhibition of protein synthesis of EL-4 cells, which express the Thy 1.2 antigen anti-Thy 1.2-ricin is equally as toxic as ricin on a molar basis. The hybrid protein toxicity is unchanged in the presence of 100 mM lactose, whereas unmodified ricin toxicity is reduced to 1% of its toxicity in the absence of lactose. This demonstrates the altered receptor specificity of the ricin hybrid. The cell-type specificity of the anti-Thy 1.2-ricin inhibition of protein synthesis correlates with the presence of the Thy 1.2 antigen. Anti-Thy 1.2-ricin at 4 microgram/ml in the presence of lactose inhibits protein synthesis within 3.5 hr by 60-80% in EL-4 cells but does not affect Thy 1.1 alloantigen and HeLa cells that lack the Thy 1 antigen. Anti-Thy 1.2-ricin in the presence of lactose selectively kills EL-4 cells at concentrations that do not kill AKR-K36 cells. This selectivity, expressed as the ratio of anti-Thy 1.2-ricin concentrations required to kill 40% of both cell types, is 700. Ricin-monoclonal antibody hybrids of this type combine a high degree of cell-type selectivity and toxicity and may have pharmacologic utility as antitumor reagents.

https://www.pnas.org/content/pnas/77/9/5483.full.pdf

Anti-Thy 1.2 monoclonal antibody linked to ricin is a potent cell-type-specific toxin

Specificity of 5lCr-Release Cytotoxicity of Lymphocytes Immune to Murine Sarcoma Virus

Cytotoxic antibody to a plasma cell tumor antigen was produced in syngeneic BALB mice by immunization with viable or inactivated plasma cell tumors. Antibody with the same specificity was found in the sera of normal BALB and other strains of mice. This natural antibody reacted with an antigen with characteristics indistinguishable from the previously described alloantigen, PC.1, and with viral envelope antigen, χVEA. The incidence of cytotoxic reactivity and the antibody titers reached a peak in normal BALB mice at 3–4 months of age, and were lower in 9–12-month old mice. The sera of germfree mice had lower reactivity; but when the mice were transferred to conventional conditions, their sera soon became as active as those of conventional mice.

A virus common to all plasma cell tumors, which is present in latent form in some normal tissues of BALB and other PC.1 positive strains, is suggested as the cause for the PC.1 antigen and for the appearance of natural antibody to it. The considerable evidence for the close association of a virus with plasma cell tumors is presented.

/pdf/immune-and-natural-antibodies-to-syngeneic-murine-plasma-9hgwp7qp49.pdf

Immune and natural antibodies to syngeneic murine plasma cell tumors.

Analysis by Immunoelectron Microscopy of Type-C Viruses Associated With Primary and Short-Term Transplanted Mouse Plasma Cell Tumors

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Specificity of 5lCr-Release Cytotoxicity of Lymphocytes Immune to Murine Sarcoma Virus

Immune and natural antibodies to syngeneic murine plasma cell tumors.

Analysis by Immunoelectron Microscopy of Type-C Viruses Associated With Primary and Short-Term Transplanted Mouse Plasma Cell Tumors