A new transmissible AIDS-like disease in mice induced by alloimmune stimuli

Gut commensal bacteria enhance pathogenesis of a tumorigenic murine retrovirus

The influence of the microbiota on viral transmission and replication is well appreciated. However, its impact on retroviral pathogenesis outside of transmission/replication control remains unknown. Using murine leukemia virus (MuLV), we found that some commensal bacteria promoted the development of leukemia induced by this retrovirus. The promotion of leukemia development by commensals is due to suppression of the adaptive immune response through upregulation of several negative regulators of immunity. These negative regulators include Serpinb9b and Rnf128, which are associated with a poor prognosis of some spontaneous human cancers. Upregulation of Serpinb9b is mediated by sensing of bacteria by the NOD1/NOD2/RIPK2 pathway. This work describes a mechanism by which the microbiota enhances tumorigenesis within gut-distant organs and points at potential targets for cancer therapy.

Replication of beta- and gammaretroviruses is restricted in I/LnJ mice via the same genetic mechanism

Mice of the I/LnJ inbred strain are unique in their ability to mount a robust and sustained humoral immune response capable of neutralizing infection with a betaretrovirus, mouse mammary tumor virus (MMTV). Virus-neutralizing antibodies (Abs) coat MMTV virions secreted by infected cells, preventing virus spread and hence the formation of mammary tumors. To investigate whether I/LnJ mice resist infection with other retroviruses besides MMTV, the animals were infected with murine leukemia virus (MuLV), a gammaretrovirus. MuLV-infected I/LnJ mice produced virus-neutralizing Abs that block virus transmission and virally induced disease. Generation of virus-neutralizing Abs required gamma interferon but was independent of interleukin-12. This unique mechanism of retrovirus resistance is governed by a single recessive gene, virus infectivity controller 1 (vic1), mapped to chromosome 17. In addition to controlling the antivirus humoral immune response, vic1 is also required for an antiviral cytotoxic response. Both types of responses were maintained in mice of the susceptible genetic background but congenic for the I/LnJ vic1 locus. Although the vic1-mediated resistance to MuLV resembles the mechanism of retroviral recovery controlled by the resistance to Friend virus 3 (rfv3) gene, the rfv3 gene has been mapped to chromosome 15 and confers resistance to MuLV but not to MMTV. Thus, we have identified a unique virus resistance mechanism that controls immunity against two distinct retroviruses.

Effect of bovine lactoferrin on a transmissible AIDS-like disease in mice

The effect of bovine lactoferrin (bLF) was examined on an AIDS-like disease (ALD) in mice. Induction of disease was achieved by inoculation with infected cell-free plasma from diseased mice to uninfected ones. The effect of treatment with bLF was investigated when administered simultaneously with the virus, 20 days prior to infection, or 20 days after infection. Animals underwent clinical surveillance and enumeration of white blood cells (WBC) and lymphocytes, as well as fluorescent staining of CD4 and CD8 bearing cells. Simultaneous administration of bLF and virus did not affect the pattern of ALD progress along the course of the experiment. Pretreatment with bLF prior to virus inoculation abolished on day 21 the detrimental effect of viral infection that lasted for two months. An opposite outcome was observed when bLF was administered 20 days after the virus. It seems that bLF had played a preventive role for a restricted period of time. However, an adverse response was elicited when bLF was administered 20 days after viral infection.

Characterization of a novel murine retrovirus mixture that facilitates hematopoiesis

A new virus previously arose in BALB/c females mated repeatedly to C57BL/6 (B6) males and then injected with fixed, activated B6 male spleen cells (V. S. Ter-Grigorov, O. Krifuks, E. Liubashevsky, A. Nyska, Z. Trainin, and V. Toder, Nat. Med. 3:37-41, 1997). In the present study, BALB/cJ mice inoculated with virus-containing plasma from affected mice developed splenomegaly, which was caused by increased numbers of Sca-1(+) Lin(-) hematopoietic stem cells (HSC) and their differentiated progeny. Biological and molecular analyses of a new virus revealed a mixture of murine leukemia viruses (MuLVs). These MuLVs comprised ecotropic and mink lung cell focus-forming (MCF) virus classes and are termed Rauscher-like MuLVs because they bear numerous similarities to the ecotropic and MCF viruses of the Rauscher MuLV complex but do not include a spleen focus-forming virus. The ecotropic virus component alone transferred some disease characteristics, while MCF virus alone did not. Thus, we have described a novel virus mixture, termed Rauscher-like MuLV, that causes an increase in hematopoiesis due to activation of pluripotent HSC. Experiments using mice and a protocol that replicated the pregnancy and immunization strategy of the original experiment demonstrated that endogenous BALB/c mouse ecotropic and xenotropic MuLVs are activated by these treatments. Emv1 was expressed in the spleens of multiparous mice but not in those of virgin mice, and Bxv1Emv1-pseudotyped MuLVs were recovered following injection of fixed, activated B6 cells. Thus, multiple pregnancies and allostimuli appear to have provided the signals required for activation of and recombination among endogenous viruses and could have resulted in generation of the Rauscher-like MuLV mixture.

HIV gp120 plus specific peptides are recognized in a similar manner to specific HLA plus peptide by HLA-restricted antigen-specific T-cell lines

HIV induces disease only following chronic activation of the immune system. Other retroviruses such as the mouse mammary tumour virus (MMTV) activate a large percentage of T cells by encoding a superantigen (SAg). To date there is no evidence that HIV encodes a SAg. An alternative way to induce pan-activation of the immune system is by allogeneic stimulation, which occurs following transplantation. Here we extend previous work which demonstrated that HIVpg120 could bind peptides in a similar manner to HLA, by demonstrating that human antigen presenting cells (APCs) expressing gp120 (but not DR1) can present a DR1-restricted peptide to induce proliferation of a DR1-restricted peptide-specific T-cell line in a similar manner to the same peptide presented by a DR1 expressing APC. Our data provide strong support for the hypothesis that the HLA-like regions of gp120 encode functional properties shared with HLA, and could explain the extraordinary clinical and immunological similarities between AIDS and chronic graft versus host disease.

Pregnancy, HLA allogeneic challenge, and implications for AIDS etiology

Because of the large HLA genetic polymorphism, a human fetus usually has several paternal HLA antigens allogeneic to its mother. The maternal gamma-immunoglobulin (IgG) antibody response to fetal HLA alloantigens is noncytotoxic and associated with local suppression of maternal cell-mediated immunity (CMI) at the maternal-fetal interface. When mother and fetus are syngeneic for most HLA antigens, an increased risk exists for a maternal anti-placental cytotoxic CMI responses, compromising fetal survival. Local suppression of maternal CMI by an anti-HLA IgG response may have evolved to protect the fetoplacental unit from a maternal CMI cytotoxic reaction against expressed developmental neoantigens. A negative aspect of this adaptive response is that infectious organisms bearing HLA-homologous alloantigens (e.g. human immunodeficiency virus type 1, HIV-1) may generate a systemic IgG response suppressing CMI. Findings are reviewed suggesting this is an etiologic factor in the acquired immune deficiency syndrome (AIDS).

The presence of antibodies against HIV peptides in the sera of alloimmune mice and thalassemic patients is due to a polyclonal activation mechanism

This paper analyses the HIV-1 gp120 epitope specificity and activation mechanisms (i.e., polyclonal versus oligoclonal) of antibodies present in the sera of alloimmune mice and humans. Sera from CBA mice engrafted with C57BL/6 lymphoid cells significantly reacted against the gp120-derived peptide as 261-270, which shares high homology with the membrane-proximal domain of HLA class II beta-chains (HLA/ gp120) and against the HIV gp120 V3 loop-derived peptides DP32 (HIV-1 MN-derived as 302-334) and C53 (HIV-1 IIIB-derived as 304-318). The same sera also reacted against the HIV-unrelated peptide necdin. Moreover, sera from BALB/c mice injected with LPS presented antibodies reacting against both HIV-related and -unrelated peptides, suggesting that similar mechanisms are shared in alloimmune and LPS-treated mice. A similar analysis was then performed on the sera of patients affected with beta-thalassemia major, receiving at least 10 blood transfusions/year. In particular, 15 of 58 (26%) sera from HIV-uninfected thalassemic patients showed a significantly reactivity against the HLA/gp 120-derived peptides. Moreover, 22 of 58 (38%) sera from the same cohort showed a significant reactivity against DP32 peptide. This reactivity was related to a polyclonal activation mechanism since the DP32-reactive sera significantly bound a panel of HIV-unrelated peptides, as observed by testing 22 sera against necdin, 21 against HSP65 kDa, 21 against amyloid-1, and 17 against MAGE-1 peptides. Moreover, a significant increase of IgG concentration was also observed in all thalassemic sera, when compared to healthy controls, without regard to the anti-gp120 antibody reactivity. Taken together, these results indicate that (i) allogeneic stimuli may induce anti-gp120 antibodies in CBA and in 38% of polytransfused patients and (ii) this reactivity is related to a polyclonal activation mechanism but not to a heightened concentration of IgG.