NK Cell-depleted Mice Research Articles

A Role for NK Cells as Regulators of CD4+ T Cells in a Transfer Model of Colitis

Previous studies have shown that the chronic inflammation observed in the colon of IL-10-deficient (IL-10(-/-)) mice is mediated by CD4+ Th1 T cells and is dependent on the presence of IFN-gamma for its initial development. As CD4+ T cells from IL-10(-/-) mice will cause colitis when transferred into recombinase-activating gene (Rag)-deficient recipients, we considered the possibility that the recipients' NK cells could be an important source of IFN-gamma for the development of colitis. Therefore, the ability of IL-10(-/-) CD4+ T cells to cause colitis in Rag-deficient recipients that had been depleted of NK cells was tested. Contrary to our expectations, NK cell-depleted recipients of IL-10(-/-) CD4+ T cells developed accelerated disease compared with nondepleted recipients. Furthermore, CD4+ T cells from normal mice (IL-10(+/+)) also caused colitis in NK cell-depleted recipient mice, but not in nondepleted recipients. NK cells inhibited effector CD4+CD45RBhigh T cells, and subsequent experiments showed that this effect was dependent on perforin. Thus NK cells can play an important role in down-regulating Thl-mediated colitis by controlling the responses of effector T cells to gut bacteria.

Establishment of a Xenogeneic Chimera without GVHD in NK Cell-Depleted SCID Mice by Grafting Rat Fetal Liver Cells

Rat lymphopoiesis did not develop when naive SCID mice were transplanted with rat fetal liver cells. However, when SCID mice were depleted of NK cells by administration of anti-murine IL-2Rβ mAb before transplantation, remarkable reconstitution of both rat T and B cells was observed in these mice without any evidence of graft-versus-host disease macroscopically or histologically. T cells in these reconstituted mice proliferated well in response to Con A and third-party rat and mouse antigens, whereas no response was seen to the stimulation with either donor rat- or host mouse-type cells. When these xenogeneic chimera mice had been immunized with SRBC, these mice exhibited DTH reaction and antibody production against the homologous antigen. These results indicate that rat fetal liver cells can differentiate to functional T and B cells in the xenogeneic microenvironment of SCID mice, if host NK cells are depleted beforehand. These rat-type T cells develop within SCID thymuses and acquire tolerance to either donor F344 rat or host SCID mouse antigens.

Role of NK cells in immunomodulator-mediated resistance to herpesvirus infection

Seven chemically diverse biological response modifiers (BRM) were compared for antiviral activity in intact and NK cell-depleted CD-1 mice. Both spontaneous and BRM-induced splenic NK cell cytotoxicity were depleted for at least 5 days following treatment with the monoclonal antibody NK1.1. Antiviral protection of standard doses of MVE-2, pIC, pICLC, rmIFN-τ and CL246, 738 against lethal MCMV or HSV-2 infections was not abrogated by NK cell depletion, demonstrating that NK cells are not required for BRM-induced antiviral activity against these herpesviruses. When mice were treated with 100000 U of rHuIFN-α B/D, NK cells were not required for activity against MCMV, while at a dose of 25000 U, NK cells appeared to be partially required against MCMV. At lower doses, the activity of rHuIFN-α B/D against MCMV appeared dependent upon the presence of NK cells. A similar dose-related requirement for NK cells was observed for activity of OK-432. Thus, at higher doses of rHuIFN-α B/D and OK-432, elements of the natural immune system in addition to or other than NK cells are apparently involved, while at lower doses NK cells appear to play a more important role in antiviral protection against MCMV infection.

Mouse Hypersensitivity Pneumonitis: Depletion of NK Cells Abrogates the Spontaneous Regression Phase and Leads to Massive Fibrosis

The contribution of natural killer cells (NK) in the progression of mouse hypersensitivity pneumonitis induced by repeated intranasal instillations with the thermophilic actinomycete Faeni rectivirgula was examined. These instillations determined a very large increase in the lung index (ca. twofold at 3 weeks), used as a measure of inflammation. In addition, this instillation was associated with a tenfold increase in the number of cells recovered in the bronchoalveolar lavage (BAL) at 3 weeks and thereafter. Most of these cells were macrophages, whereas T lymphocyte numbers increased at 6 weeks and thereafter. The instillations were also associated with a substantial fibrotic response in the lungs, as seen by large increases in hydroxyproline levels in the lungs. This fibrotic response, however, diminished after 6 weeks of instillations. Similarly, examination of histological preparations of lungs of challenged mice showed that F. rectivirgula induced inflammatory infiltrates of macrophages, lymphocytes, and neutrophils. The severity of the lesions were reduced in mice given more than 6 weeks of the actinomycete challenge. The involvement of NK cells on the development of this pulmonary pathology was determined by infusing F. rectivirgula-challenged mice with anti-NK 1.1 antibody. The depletion protocol was validated by verifying that such treatments effectively blocked lung NK cell activity. Such NK cell-depleted mice responded to the F. rectivirgula challenge with an increased lung index at 9 and 12 weeks, compared to mice challenged with F. rectivirgula and given control antibody. NK cell-depleted mice also responded to the actinomycete with a superior cellular recruitment in the BAL, with this increase mostly mediated by macrophages. Similarly, NK cell-depleted mice developed a fibrotic response that was much higher than that seen in control challenged mice, at 6, 9, and 12 weeks after initiation of the transnasal instillations. This was corroborated by scoring the severity of the histopathological lesions, which showed that NK cell-depleted mice had more severe lesions than challenged control mice. The importance of NK cells was confirmed by demonstrating that mice given anti-NK 1.1, challenged with F. rectivirgula and reconstituted with Percoll gradient-enriched lung NK cells had hydroxyproline levels at 9 and 12 weeks that were comparable to that seen in intact mice, as well as a histopathological score similar to control challenged mice. Overall, this suggests that in the course of a pulmonary inflammatory response, NK cells exert a suppressive effect on cellular recruitment in the BAL, contribute to down-regulating the inflammatory response, and are involved in blocking the appearance of fibrosis.

Immunobiology of infection with recombinant vaccinia virus encoding murine IL-2. Mechanisms of rapid viral clearance in immunocompetent mice.

CD8+ cytotoxic T (Tc) lymphocytes mediate recovery from vaccinia virus (VV) infection. In mice, anti-VV Tc cells are detectable on or after day 3 after infection, and cytolytic activity peaks between days 5 and 6. A rVV encoding murine IL-2, VV-hemagglutinin (HA)-IL-2, was cleared more rapidly, compared with a control rVV, VV-HA-thymidine kinase (TK), from tissues of infected euthymic normal mice. The mechanism of VV-HA-IL-2 clearance was operative early in infection and correlated with an elevated NK cell response, before the induction of anti-VV Tc cell response. We have investigated the roles of NK cells, T cells, and IFN-gamma in the rapid clearance of VV-HA-IL-2, by using specific mAb. Depletion of NK cells with mAb significantly enhanced VV-HA-IL-2 but not VV-HA-TK titers 3 days after infection. NK cells alone could not account for rapid viral clearance, because VV-HA-IL-2 titers in NK cell-depleted mice were not comparable to VV-HA-TK titers. Treatment with a mAb to IFN-gamma completely abrogated the IL-2-induced mechanism(s) of VV-HA-IL-2 clearance, and titers of the IL-2-encoding virus were comparable to control virus titers. In addition, the elimination of CD4+ but not CD8+ T cells resulted in significant increases in VV-HA-IL-2 titers.

Adoptive transfer of natural killer cell activity in B6D2F1 mice challenged with Salmonella typhimurium

The purpose of this study was to extend our previous findings as to the role of murine NK cells in host protection to a challenge infection with virulent Salmonella typhimurium SR-11. B6D2F1 mice were depleted of NK cells with anti-asialo GM1 or a monoclonal antibody, anti-NK 1.1, followed by a salmonellae challenge. Significantly decreased numbers of splenic bacteria ( P < 0.005) in the NK cell-depleted mice were noted at 12, 24, and 48 hr postchallenging, compared to the sham-injected control animals. When Percoll gradient-enriched large granular lymphocytes (NK cells) were adoptively transferred to NK cell-depleted mice followed by challenging, the splenic bacterial numbers were comparable to those present in NK cell-intact, control mice. These data indicate that large granular lymphocytes (NK cells) are responsible for the down-regulation of the protective host response in mice challenged with the facultative intracellular parasite, S. typhimurium.

Role of natural killer cells in experimental murine myocarditis

Infection of adolescent CD-1 mice with CVB3 activates NK cells. These activated NK cells can lyse infected fibroblasts in vitro and their transfer into mice prior to inoculation with CVB3 can reduce virus titers in heart tissues. If mice are depleted of NK cells prior to and throughout a CVB3 infection, myocarditic lesions show a comparatively greater pathology in the form of severe dystrophic calcification than in infected mice with an intact NK cell system. Also NK cell-depleted mice have significantly higher virus titers in heart tissues. These data suggest a role for NK cells in the infected mouse, i. e., that they reduce virus titers through lysis of infected cells and thereby reduce the severity of myocarditis. In keeping with such a defensive role is the finding of NK cells among the first inflammatory cells forming the nascent CVB3-induced focal myocarditic lesion. Paradoxically, NK cells remain in the mature lesion up to 10 days p.i. and may thus contribute to pathology. Further studies on whether these long-term residents release cytotoxic factors which continue to damage myocytes in absence of significant virus titers in heart tissues must be performed. These studies are now feasible because of the recent development of monoclonal antibodies against NK cytotoxic factor [30]. Finally, diet can adversely effect generation of activated NK cells in CVB3-inoculated mice and this finding may have significance for health-conscious human beings.