Split tolerance between spleen and lymph node cells in severe combined immunodeficiency mice grafted with AKR fetal liver cells

Breakdown of peripheral T-cell tolerance by chronic interleukin-15 elevation

Thymic deletion purges the repertoire of most developing T cells with the potential for overt self-reactivity, but some self-specific cells do emerge into the peripheral pool. Under most conditions, these potentially autoaggressive cells remain in a quiescent state. However, in some circumstances, they become activated and acquire effector function, leading to immune disease. It is thus important to clarify the mechanism(s) responsible for determining the balance between such inappropriate T-cell activation and the normal state of peripheral tolerance. In this article, we show that chronic elevation of interleukin-15 levels interferes with the tolerant state of CD8+ T cells through a process that involves activation of nonlymphoid antigen-presenting cells by CD4+asialo-GM1+ (ASGM1) or both CD4+ASGM1- and CD4-ASGM1+ cells. These findings suggest a potential role for dysregulated interleukin-15 production in promoting tolerance breakdown. This new information may be of potential use in improving tumor vaccines to self-antigens and in ameliorating autoimmune or graft-versus-host disease.

Total body irradiation causes profound changes in endothelial traffic molecules for hematopoietic progenitor cell recruitment to bone marrow

Nonirradiated bone marrow (BM) venules and sinusoids in murine skull support hematopoietic progenitor cell (HPC) rolling through constitutively expressed endothelial (P- and E-) selectins and VCAM-1. Using intravital microscopy, we tested whether host conditioning with total body irradiation (TBI) changes the molecular mechanisms by which murine HPCs from fetal livers (FL) interact with BM endothelial cells. Although a high dose of TBI did not affect the overall frequency of HPC rolling in BM microvessels, the underlying molecular mechanisms differed from those in nonirradiated BM. TBI induced VCAM-1 up-regulation in BM microvessels, whereas P-selectin expression was reduced and the low baseline level of E-selectin remained unchanged. Only the administration of anti-VCAM-1, but not anti-P- or -E-selectin monoclonal antibodies, decreased FL HPC rolling. Rolling was frequently followed by firm arrest (sticking), even in nonirradiated BM microvessels in which sticking was entirely pertussis toxin-insensitive-that is, Galpha(i)-coupled signaling events (eg, through chemokines) were apparently not required. TBI increased the frequency of sticking FL HPC. This irradiation-induced additional sticking was reversed when FL HPCs were pretreated with pertussis toxin, suggesting that TBI induced elevated expression of a Galpha(i)-protein-coupled chemotactic signal in the BM. This chemoattractant was probably distinct from SDF-1alpha because, unlike adult HPCs, FL HPCs (day 11 of gestation) responded poorly to SDF-1alpha in vitro. These results demonstrate that TBI induces profound changes in the expression of endothelial traffic molecules in the BM, and they indicate that FL HPCs can home to the BM in the absence of SDF-1alpha and other Galpha(i)-protein-coupled signals.

Immune responses of interferon gamma (IFN-gamma) knock out mice to repeated Haemaphysalis longicornis (Acari: Ixodidae) nymph infestations

To investigate the immunological mechanisms of acquired resistance to tick infestation, interferon gamma (IFN-gamma) deficient mice (IFN-gamma mice) were used to assess interleukin-4 (IL-4) and antibody production levels against tick salivary gland antigen on three successive infestations with Haemoaphysalis longicornis Neumann nymphs. The engorged body weight of the ticks decreased during the second and third infestations. Similar observations were noted in IFN-gamma+/+ mice. However, the engorged body weight of the ticks from IFN-gamma +/+ mice were considerably lower than those from IFN-gamma-/- mice. A marked increase in antibody production during the second and third infestations was observed indicating that IFN-gamma-/- mice could acquire immunological resistance against H. longicornis nymphs. Moreover, IL-4 levels were higher during the first and third infestations but decreased during the second infestation. IL-4 levels were significantly higher in IFN-gamma-/- mice than in IFN-gamma+/+ mice. We have shown here that the statistically significant high IL-4 levels observed in IFN-gamma-/- mice may be a result of type 2 helper cell (Th2) polarization. However, the apparently higher IL-4 levels during the first and third infestations and the notable decline during the second infestation suggest that other cytokines or factors in the host immune system may play a part in regulating IL-4 levels.