Soluble factors in tolerance and contact sensitivity to DNFB in mice. VII. Characterization of a monoclonal, efferent-acting suppressor factor with specificity for DNP/H-2Kd

To study further soluble factors which regulate contact sensitivity (CS) to 2,4-dinitrofluorobenzene (DNFB), hapten-primed spleen cells from BALB/c mice were used to make T-cell hybridomas. A hybrid constitutively producing a suppressor factor was identified and cloned (clone 3-10). Incubation of BALB/c DNFB immune lymph node cells (LNC) in the 3-10 supernatant suppressed the ability of the immune cells to transfer CS to DNFB. The passive transfer of CS to oxazalone or to 2,4,6-trinitrochlorobenzene (TNCB) was not suppressed by the 3-10 factor. The hapten specificity of the 3-10 factor further was demonstrated by the ability of DNFB immune LNC but not LNC from unsensitized or from TNCB-sensitized mice to absorb the factor. The 3-10 factor also was adsorbed by DNFB-immune LNC from mice that were syngeneic with BALB/c mice at the K locus of the MHC (e.g., B10.D2 and D2.GD). Pretreatment of DNFB-immune LNC with monoclonal anti-Kd antibody or with anti-DNP antibodies blocked the ability to adsorb the factor. These results indicated that the 3-10 suppressor factor binds to DNP/H-2Kd complexes on immune LNC. Nylon wool-purified T cells (83% Thy-1.2+) from DNFB-immune LNC were able to adsorb the factor as well as unseparated immune LNC. Furthermore, treatment of immune LNC with anti-Thy-1.2 plus C' abrogated the ability of the cells to adsorb the factor, indicating that the cellular target of the 3-10 factor is a T cell. In addition, treatment of the immune LNC with an autoantiidiotypic antiserum (CS 231) plus C', which depletes DNP-specific delayed-type hypersensitivity effector T (TDH) cells, also abrogated the ability of the cells to adsorb the factor. Finally, the suppressor factor was adsorbed and eluted from DNP affinity columns but was not adsorbed by TNP affinity columns. Collectively, these results indicate that although the monoclonal 3-10 suppressor factor has affinity for DNP, focusing of the factor on the TDH cells requires recognition of DNP in the context of the appropriate MHC determinant, Kd.     

Presentation of antigenic peptides by products of the major histocompatibility complex

Molecules encoded by the major histocompatibility complex (MHC) are polymorphic integral membrane proteins adapted to the presentation of peptide fragments of foreign antigens to antigen-specific T-cells. The diversity of infectious agents to which an immune response must be mounted poses a unique problem for receptor–ligand interactions; how can proteins whose polymorphism is necessarily limited bind an array of peptides almost infinite in its complexity? Both MHC class I and class II determinants have achieved this goal by harnessing a limited number of peptide side chains to anchor the epitope in place while exploiting conserved features of peptide structure, independent of their primary sequence. While class I molecules interact predominantly with the N- and C-termini of peptides, class II determinants form an extensive hydrogen bonding network along the length of the peptide backbone. Such a strategy ensures high-affinity binding, while selectively exposing the unique features of each ligand for recognition by the T-cell receptor. © 1998 European Peptide Society and John Wiley & Sons, Ltd.     

Alloreactive T cell responses and acute rejection of single class II MHC-disparate heart allografts are under strict regulation by CD4+ CD25+ T cells

Skin but not vascularized cardiac allografts from B6.H-2bm12 mice are acutely rejected by C57BL/6 recipients in response to the single class II MHC disparity. The underlying mechanisms preventing acute rejection of B6.H-2bm12 heart allografts by C57BL/6 recipients were investigated. B6.H-2bm12 heart allografts induced low levels of alloreactive effector T cell priming in C57BL/6 recipients, and this priming was accompanied by low-level cellular infiltration into the allograft that quickly resolved. Recipients with long-term-surviving heart allografts were unable to reject B6.H-2bm12 skin allografts, suggesting potential down-regulatory mechanisms induced by the cardiac allografts. Depletion of CD25+ cells from C57BL/6 recipients resulted in 15-fold increases in alloreactive T cell priming and in acute rejection of B6.H-2bm12 heart grafts. Similarly, reconstitution of B6.Rag(-/-) recipients with wild-type C57BL/6 splenocytes resulted in acute rejection of B6.H-2bm12 heart grafts only if CD25+ cells were depleted. These results indicate that acute rejection of single class II MHC-disparate B6.H-2bm12 heart allografts by C57BL/6 recipients is inhibited by the emergence of CD25+ regulatory cells that restrict the clonal expansion of alloreactive T cells.     

Hapten application to the skin induces an inflammatory program directing hapten-primed effector CD8 T cell interaction with hapten-presenting endothelial cells

Contact hypersensitivity is a CD8 T cell-mediated response to hapten sensitization and challenge of the skin. Effector CD8 T cell recruitment into the skin parenchyma to elicit the response to hapten challenge requires prior CXCL1/KC-directed neutrophil infiltration within 3-6 h after challenge and is dependent on IFN-γ and IL-17 produced by the hapten-primed CD8 T cells. Mechanisms directing hapten-primed CD8 T cell localization and activation in the Ag challenge site to induce this early CXCL1 production in response to 2,4-dinitrofluorobenzene were investigated. Both TNF-α and IL-17, but not IFN-γ, mRNA was detectable within 1 h of hapten challenge of sensitized mice and increased thereafter. Expression of ICAM-1 was observed by 1 h after challenge of sensitized and nonsensitized mice and was dependent on TNF-α. The induction of IL-17, IFN-γ, and CXCL1 in the challenge site was not observed when ICAM-1 was absent or neutralized by specific Ab. During the elicitation of the contact hypersensitivity response, endothelial cells expressed ICAM-1 and produced CXCL1 suggesting this as the site of CD8 T cell localization and activation. Endothelial cells isolated from challenged skin of naive and sensitized mice had acquired the hapten and the ability to activate hapten-primed CD8 T cell cytokine production. These results indicate that hapten application to the skin of sensitized animals initiates an inflammatory response promoting hapten-primed CD8 T cell localization to the challenge site through TNF-α-induced ICAM-1 expression and CD8 T cell activation to produce IFN-γ and IL-17 through endothelial cell presentation of hapten.     

A PHYSIOLOGICAL INVESTIGATION OF THE HOT SPRING DIATOM,ACHNATHES EXIGUA GRÜN1

The diatom Achnanthes exigua, isolated from Alhambra North Hot Spring, showed a maximum growth rate of 2 doublings per day at 40 C; the maximum and minimum temperatures at which growth occurred was 44 and 10 C, respectively. The optimal temperature for respiration was 40 C, whereas the optimum temperature for photosynthesis was 42 C. Respiration exhibited greater thermotolerance than either growth or photosynthesis. Light saturation occurring at comparatively low light intensities suggests that the unialgal diatom culture may represent a selected shade-adapted organism.     

Population responses of plant-associated invertebrates to foraging by largemouth bass fry (Micropterus salmoides)

The effect of foraging by largemouth bass fry (Micropterus salmoides) upon invertebrates associated with aquatic macrophytes was determined using six 4 m² exclosures in Cochran Lake, Michigan during June 1978. The cladoceranSida crystallina rapidly declined in exclosures with fry, but increased in control exclosures without fry. Chironomids and chydorids showed little change in the exclosures.Invertebrate populations and foraging by fry were also monitored in the lake during 1976 and 1979.Sida declined rapidly in June of both years. In 1979, a decline from 2.2 × 10³ to 0.3 × 10³ individuals per m² and a sharp drop in the proportion of adults between 19 and 22 June coincided with the entry of a large school of fry into the study site on 19 June. Chironomids also declined during June of both years, while chydorids became increasingly abundant in mid-summer and showed no evidence of depletion by the fish.These results suggest that populations of certain prey, which are found locally in high densities in the littoral zone, may be highly susceptible to brief episodes of intense predation by fish fry.