Genetically modified animals and immunodeficiency

Autoimmune ovarian disease in day 3-thymectomized mice: the neonatal time window, antigen specificity of disease suppression, and genetic control

Discovery of the CD4+CD25+ T cells has stemmed from investigation of the AOD in the d3tx mice. Besides CD4+CD25+ T cell depletion, d3tx disease induction requires effector T cell activation prompted by lymphopenia. This is supported by other neonatal AOD models in which T cell-mediated injury has been found to be triggered by immune complex or Ag immunization. In addition, there is growing evidence that support a state of neonatal propensity to autoimmunity, which depends on concomitant endogenous antigenic stimulation, concomitant nematode infection, resistance to CD4+CD25+ T cell regulation, and participation of the neonatal innate system. The suppression of d3tx disease by polyclonal CD4+CD25+ T cells appears to be dependent on endogenous Ag and the persistence of regulatory T cells. Thus, suppression of AOD occurs in the ovarian LN, and AOD emerges upon ablation of the input regulatory T cells; and in AIP, the hormone-induced expression of prostate Ag in the CD4+CD25+ T cell donors rapidly enhances the capacity to suppress disease over Ag negative donors. Finally, genetic analysis of AOD and its component phenotypes has uncovered seven Aod loci. As the general themes that emerged, significant epistatic interactions among the loci play a role in controlling disease susceptibility, the majority of the Aod loci are linked to susceptibility loci of other autoimmune diseases, and the genetic intervals encompass candidate genes that are differentially expressed between CD4+CD25+ T cells and other T cells. The candidate genes include Pdcd1, TNFR superfamily genes, H2, Il2, Tgfb, Nalp5 or Mater, an oocyte autoAg that reacts with autoantibody in sera of d3tx mice.

THE USE OF IMMUNOCOMPROMISED ANIMALS AS MODELS FOR HUMAN SEPTIC SHOCK

Although it is generally understood that no single animal model truly reflects human sepsis, the study of sepsis in immunocompromised animals is highly relevant to human sepsis research. The majority of patients with severe sepsis have significant underlying diseases that may alter innate immune defenses, disrupt microbial clearance mechanisms, and complicate the pathophysiology of human sepsis. Septic shock itself has significant effects upon the innate and adaptive host immune responses that may contribute to a state of sepsis-induced immune dysregulation. A number of animal models of sepsis displaying an array of immunocompromised states are now available. Most of these systems are small animal models with genetically defined defects of immune defenses or acquired defects from receipt of immunosuppressive or myeloablative agents. Greater emphasis should be placed on preclinical models of immunocompromised animals in the future to assess the potential clinical utility of novel drugs for human septic shock.

Scheduled kinetics of cell proliferation and phenotypic changes during immature thymocyte generation

Precursor CD4-CD8- (DN) thymocytes rearrange their TCR-beta genes, and only those which succeed in beta-selection subsequently expand and differentiate into immature CD4+CD8+ (DP) thymocytes. The cell subsets corresponding to the successive steps of this transition can be defined in terms of CD44 and CD25 expression. We partially synchronized the differentiation process by eliminating cycling cells with the anti-mitotic agent demecolcine. Using in vivo pulse labeling with bromodeoxyuridine, we determined the order of entry into DNA synthesis of the different DN and transitory (CD4-/lo CD8+) cell subsets. Two independent proliferation phases were identified. The first cells to enter the cell cycle were CD44-CD25lo, and CD4/CD8/TCR-/BrdU four-color staining showed that they all expressed a low density of the TCR-beta chain, an element of the pre-TCR (the TCR-alpha locus is still in germ-line configuration at this stage). Cycling of CD44+CD25+ cells was detected later, and no starting point was observed at the CD44-CD25hi stage. CD8 expression was immediately detectable in cycling cells, but they took 24 h to reach the DP stage. The study of TCR-Calpha-deficient mice showed that beta gene rearrangement occurred once proliferation had ceased at the DP stage, and that it had no influence on the DN-DP transition. These data show that precursor thymocytes undergo two independent waves of expansion, and that the second wave is restricted to cells capable of pre-TCR expression.

Delayed-type hypersensitivity response to high doses of adenoviral vectors

The present study evaluates the hypothesis that delayed-type hypersensitivity (DTH) contributes to the inflammatory reaction observed when high-dose adenoviral (Ad) vectors are administered to a previously immunized animal. Immunocompetent C57BL/6 mice immunized intraperitoneally with 10(9) pfu AdCMV.Null [an E1-, E3- Ad vector with a cytomegalovirus (CMV) promoter but no transgene] and challenged intradermally to the footpad with the same vector demonstrated significant footpad swelling 24 hr after challenge with 10(9) pfu, but not with a lower dose. Footpad histology revealed a mononuclear-granulocytic cellular infiltrate typical of that seen in DTH. Evaluation of the same doses of vector in immunodeficient mice nu/nu and RAG-2- on the C57BL/6 background, and nu/nu and severe combined immunodeficiency (SCID) on the BALB/c background demonstrated suppression of footpad swelling. However, the footpad response remained intact in beta 2-microglobulin deficient (beta 2-m-) mice, suggesting minimal or no role of major histocompatibility complex (MHC) class I-mediated mechanisms for the region of localized inflammation. Challenge with an Ad expressing the interleukin-2 cDNA to immunized C57BL/6 mice demonstrated augmented footpad swelling response. Finally, pretreatment with cyclosporin resulted in a 69% inhibition of the response compared to controls, whereas other immunosuppressants (cyclophosphamide, methotrexate, and hydrocortisone) had no inhibitory effect. These findings provide further insight into the dynamic interplay of immune processes ultimately leading to inflammation when high-dose Ad vectors are administered to a target organ.

Ig VH-dependent interaction between immunoglobulins and CD4

CD4 interacts with the immunoglobulin (Ig)-VH domains by a virtue of its solvent-exposed C and C strands. These two strands also contribute to the full HIV-gp120 binding and participate significantly in binding to class II MHC molecules. In this paper we hypothesize that any high-affinity interaction between serum (or membrane-expressed) Ig and CD4 may have impact on early T cell activation events. The existing data provide evidence for different outcomes of a high affinity Ig/CD4 interaction on T cell proliferation and cytokine secretion: costimulation and inhibition. We will also discuss how a low affinity CD4/Ig interaction could play an important role in B cell stimulation initiated through surface Ig receptors, and how CD4 may be involved in shaping the B cell repertoire.

Active interleukin-1 receptor required for maximal progression of acute pancreatitis

OBJECTIVE

The authors' aim was to determine the requirement for an active interleukin (IL)-1 receptor during the development and progression of acute pancreatitis.

SUMMARY OF BACKGROUND DATA

Interleukin-1 is a pro- inflammatory cytokine that has been shown to be produced during acute pancreatitis. Earlier animal studies of moderate and severe pancreatitis have shown that blockade of this powerful mediator is associated with attenuated pancreatic destruction and dramatic increases in survival. The exact role played by IL-1 and the requirement for activation of its receptor in the initiation and progression of pancreatitis is unknown.

METHODS

Conventional and IL-1 receptor "knockout" animals were used in parallel experiments of acute pancreatitis induced by intraperitoneal injection of cerulean (50 microg/kg every 1 hour X 4). The conventional mouse strain had the IL-1 receptor blocked prophylactically by means of a recombinant IL-1 receptor antagonist (10 mg/kg injected intraperitoneally every 2 hours). The second mouse strain was genetically engineered by means of gene targeting in murine embryonic stem cells to be devoid of type 1 IL-1 receptor (IL-1 receptor knockout). Animals were killed at 0, 0.5, 1, 2, 4, and 8 hours, with the severity of pancreatitis determined by serum amylase, lipase, and IL-6 levels and blind histologic grading. Strain-specific controls were used for comparison.

RESULTS

The genetic absence of the IL-1 receptor or its pharmacologic blockade resulted in significantly attenuated pancreatic vacuolization, edema, necrosis, inflammation, and enzyme release. Serum IL-6, a marker of inflammation severity, was dramatically decreased in both groups.

CONCLUSIONS

Activation of the IL-1 receptor is not required for the development of pancreatitis but apparently is necessary for the maximal propagation of pancreatic injury and its associated inflammation.

Contribution of alpha/beta and gamma/delta T lymphocytes to immunity against Mycobacterium bovis bacillus Calmette Guérin: studies with T cell receptor-deficient mutant mice

Mutant mice with defined T cell deficiencies were infected with Mycobacterium bovis bacillus Calmette Guérin (BCG) and the relative contribution of alpha/beta T cells and gamma/delta T cells to the host immune response was assessed. Recombinase activating gene (RAG-1)-/- mutants as well as T cell receptor (TcR) beta-/-, but not TcR-delta-/-, mutants succumbed to M. bovis BCG infection and failed to develop granulomatous lesions. Antigen-induced IFN-gamma production by spleen cells in vitro was abrogated in RAG-1-/- mutants and markedly diminished in TcR-beta-/- and TcR-delta-/- mice. Reconstitution experiments suggest that both alpha/beta and gamma/delta T cells are essential for antigen-specific IFN-gamma secretion. Our data formally prove the crucial role of alpha/beta T cells and reveal accessory functions of gamma/delta T cells in optimum immunity against M. bovis BCG.

Outcome of infection with different strains of Trypanosoma cruzi in mice lacking CD4 and/or CD8

Mice lacking CD4 and/or CD8 gene expression, generated by embryonic stem-cell technology, were used to study the role of CD4+ and CD8+ cells in the resistance to the acute infection with virulent (Tulahuén and RA) or mild (CA-I) strains of Trypanosoma cruzi. The presence of both CD4+ and CD8+ cells contributed to the survival of mice infected with T. cruzi, and each T-cell subtype was able to sustain protective functions in the absence of the other one. However, in certain host-parasite combinations, CD8+ cell-independent mechanisms were able to control the parasite load. Moreover, CD8- mice chronically infected with a low virulent strain of T. cruzi were protected from an otherwise lethal challenge with the parasite. A different organ distribution of parasite nests was observed when mutant (but not wild type) animals infected with different parasite strains were compared. CD4- mice produced high levels of IgG antibodies against peptide antigens or a whole homogenate from the parasite after infection with CA-I strain. A dramatic enhancement of IgG1- and IgG2a-specific antibodies was observed.

Gene targeting of the immune system: the surprises continue

To date, an impressive number of mutant mice strains have been generated by targeted mutagenesis of the immune system. During the past year, such knockout mice have been particularly valuable in revealing the biological functions of certain cytokines and their receptors, and also in identifying cell surface molecules critical for T-cell activation. Advances in targeting technologies also figure prominently in the accomplishments of the past year, with cell type specific gene targeting representing a major refinement of current methodologies.

B-lineage differentiation in normal and transformed cells and the microenvironment that supports it

B-cell differentiation is a complex process mediated through interactions with the microenvironment of the bone marrow and fetal liver. These interactions alter patterns of gene expression and allow precursors to develop into Ig+ B cells. Recent work has shown that some of these events can be triggered in B-cell precursors transformed by Abelson virus. Other advances have refined our understanding of the role of cytokines, hormones and stromal cells in the differentiation process.

Dismantling the immune system

During the past year, we have witnessed a veritable explosion in the number of mutant mouse strains produced by gene targeting in embryonic stem cells. Many of the informative targeted mutants have relevance to the field of immunology. At least one mutant mouse strain now exists for most of the important genes in immunology, and this collection of mutant mice has greatly expanded the experimental repertoire of immunologists. New targeting techniques have been developed that have often found their first application in immunology.