Influenza viral glycoproteins induced cell-mediated cytotoxicity by an interferon-independent mechanism

Administration of inactivated and detergent-treated influenza virus to mice before virus challenge reduces mortality

Formalin-inactivated virus (FIV) and the detergent-treated virus (DTV) preparations were tested for their ability to enhance the resistance of mice to experimental influenza infection. FIV (100 micrograms) was administered intravenously to mice. After 24 hr, animals were challenged with 5 LD50 dose intranasally. FIV-treated and non-treated (control) mice had 10% and 100% mortality, respectively. Similar results were obtained with the DTV (40 micrograms) preparation. The pulmonary virus titer of FIV-treated mice was lower when compared with the control. Mechanisms other than acquired immunity may have conferred the early resistance to virus infection in mice.

Stimulation of tumor necrosis factor secretion by purified influenza virus neuraminidase

We showed that purified neuraminidase (NA) of influenza virus, but not hemagglutinin (HA), possessed the potential to increase in vitro and in vivo the interleukin 1 (IL 1) activity of mouse peritoneal macrophages. In this study, we report the effect of NA and HA on the secretion of tumor necrosis factor (TNF) activity by murine peritoneal macrophages. TNF being a cytokine sharing many related and overlapping biological functions with IL 1. The two glycoproteins of the strain A/USSR/90/77 (H1N1) were purified electrophoretically and were tested in vitro at doses ranging from 0.5 to 5.0 micrograms using the adherent peritoneal macrophages of C3H/HeN mice elicited with thioglycolate. The TNF activity of culture supernatants, collected 24 hr after stimulation with viral protein, was evaluated by the standard cytolytic assay using L929 and WEHI.164 cells. No increase of the TNF activity was observed at 0.5 micrograms of NA (4.8 Units (U)/ml in the L929 assay and 20.4 U/ml in the WEHI assay) but further increase of NA to 1.0 microgram had a significant effect on the TNF activity (39.7 and 88.8 U/ml, respectively). Higher concentrations of NA (2.0 and 5.0 micrograms) did not improve the TNF activity. The addition of a rabbit anti-TNF-alpha serum to the assay system reduced the lysis of L929 cells by 85%, suggesting that the observed activity was due to TNF. In parallel, the enhancement of IL 1 activity due to NA was reverified using D10.G4.1 cells instead of the C3H/HeJ thymocytes assay used previously. NA augmented the IL 1 activity up to 1.0 micrograms (25.8 U/ml). The addition of monoclonal anti-IL 1 antibodies (100 neutralizing units) to the supernatants reduced the incorporation of [3H]-thymidine by 90 to 95%, suggesting that the observed activity was due to IL 1. Comparative results of NA and HA showed that only NA stimulated the TNF and IL 1 activities of murine macrophages.

Human influenza virus neuraminidase, but not hemagglutinin, induces murine macrophage interleukin 1 in vivo and in vitro

Since our previous studies showed that the viral glycoproteins of influenza virus, hemagglutinin (HA) and neuraminidase (NA), are involved in stimulating the human and mouse natural killer (NK) cell activities, it was considered appropriate to study the effect of these glycoproteins on macrophages, another component of nonspecific resistance mechanisms. The glycoproteins HA and NA, of the strain A/USSR/90/77 (H1N1), were purified electrophoretically and were tested in vitro using the adherent peritoneal macrophages of C3H/HeN mice elicited with thioglycolate. IL-1 activity of culture supernatants, collected 24 h after the addition of viral proteins, was evaluated by the standard IL-1 assay using C3H/HeJ thymocytes. Viral NA, but not HA, induced a significant increase of IL-1 activity (p less than 0.05) at dilutions ranging from 1:2 (about thirty-fold augmentation) to 1:256 (nine-fold augmentation) compared to control. The in vivo data showed that intraperitoneal administration of either glycoprotein (2 micrograms) alone did not increase the IL-1 activity; but a six-fold increase (p less than 0.05) of IL-1 activity was observed when the adherent macrophages prepared from NA-primed mice (24 h and 96 h postinoculation) were restimulated in vitro with NA. Similar experiments carried out with HA showed no increase in the IL-1 activity. These and other results suggest that influenza virus NA is superior to HA in stimulating some components of the nonspecific resistance mechanisms.

Biology of natural killer cells

Studies of cytotoxicity by human lymphocytes revealed not only that both allogeneic and syngeneic tumor cells were lysed in a non-MHC-restricted fashion, but also that lymphocytes from normal donors were often cytotoxic. Lymphocytes from any healthy donor, as well as peripheral blood and spleen lymphocytes from several experimental animals, in the absence of known or deliberate sensitization, were found to be spontaneously cytotoxic in vitro for some normal fresh cells, most cultured cell lines, immature hematopoietic cells, and tumor cells. This type of nonadaptive, non-MHC-restricted cellmediated cytotoxicity was defined as “natural” cytotoxicity, and the effector cells mediating natural cytotoxicity were functionally defined as natural killer (NK) cells. The existence of NK cells has prompted a reinterpretation of both the studies of specific cytotoxicity against spontaneous human tumors and the theory of immune surveillance, at least in its most restrictive interpretation. Unlike cytotoxic T cells, NK cells cannot be demonstrated to have clonally distributed specificity, restriction for MHC products at the target cell surface, or immunological memory. NK cells cannot yet be formally assigned to a single lineage based on the definitive identification of a stem cell, a distinct anatomical location of maturation, or unique genotypic rearrangements.