Genetic basis of ultraviolet-B effects on contact hypersensitivity

The genetic basis of the effects of ultraviolet B(UVB) radiation on the induction of contact hypersensitivity (CH) to dinitrofluorobenzene (DNFB) has been explored in genetically defined mice. It was found that acute, low-dose UVB radiation produced profound depletion of epidermal Langerhans cells (LC) at UVB-treated sites in all strains of mice tested. However, when DNFB was applied to UVB radiation sites, unresponsiveness developed in some strains of mice, but vigorous contact hypersensitivity was induced in others. The UVB-susceptible phenotype proved dominant or codominant in F₁ hybrids derived from parental strains of the susceptible and UVB-resistant phenotypes. Experiments conducted in one set of F₁ hybrids derived from two UVB-susceptible parental strains displayed UVB resistance, suggesting gene complementation, and showed that more than one genetic locus was involved. Segregant backcross populations, analyzed for the capacity to develop CH after UVB treatment and skin painting with DNFB, revealed that at least two, and probably three, independent genetic loci participate in determining UVB resistance. Results of experiments with H-2 congenic and recombinant mice derived from the B10 background implicated class I genes of the major histocompatibility complex as relevant genetic factors. These results indicate that there is a dissociation between the effects of UVB radiation on epidermal Langerhans cells and the capacity of a cutaneous surface to support the induction of contact hypersensitivity. The data indicate that the induction of CH to haptens is dependent on normal numbers of functional LC at the skin painting site only in some strains of mice. The data imply that in the so-called UVB-resistant strains of mice, alternative (non-Langerhans cell-dependent) mechanisms allow for the induction of CH. Several independent genetic loci, one of which appears to be H-2, govern this UVB-related effect.     

Control of the antibody response of C57BL/6 Lyt-congenic strains to the Lyt-3.1 alloantigen by a gene linked to theLyt-2 locus

Congenic anti-Lyt-3.1 sera have recently been produced by immunizing B6-Lyt-2^a mice with thymocytes from either B6-Lyt-2^a, Lyt-3^a or B6-Lyt-2^a, Lyt-3^a, H-2^k mice (Boos et al. 1978). Surprisingly, mice of the congenic strain B6 failed to produce either anti-Lyt-2.1 or anti-Lyt-3.1 cytotoxic antibodies after identical immunizations. To determine the genetic basis for the difference in response to Lyt-3.1, (B6 × B6-Lyt-2^a)F_a mice and progeny of the backcross, (B6 × B6-Lyt-2^a)F₁ × B6-Lyt-2^a, were immunized with B6-Lyt-2^a, Lyt-3^a, H-2^k thymocytes. In addition, thymic biopsies of backcross progeny were performed and thymocytes tested for the Lyt-2.2 antigenic specificity. Results indicate that gene(s) governing the immune response to Lyt-3.1 is (are) linked to theLyt-2 locus, and that the responder allele (linked toLyt-2 ^a ) shows very poor penetrance in Lyt-2^a/Lyt-2^b mice.     

Induction, by adriamycin and mitomycin C, of modifications in lipid composition, size distribution, membrane fluidity and permeability of cultured RDM4 lymphoma cells

Adriamycin and mitomycin C were previously found to modulate the sensitivity of lymphoma cells to lysis by certain effectors of immunity and this modulation was dependent on drug concentration. In the present studies, RDM4 lymphoma cells were treated with different concentrations of the two drugs for 24 h in culture. These treatments resulted in changes in the lipid composition, membrane fluidity, cell size distribution, and permeability to 51CrO4, Trypan blue, Acridine orange and trimethylaminodiphenylhexatriene (TMA-DPH) of the cells. Changes in some of these parameters, as a function of drug concentration, resulted in dose-response curves which were bell-like shaped, hence paradoxical similarities between non-drug-treated cells and cells treated with higher drug concentrations were observed.     

Links between global taxonomic diversity,ecological diversity and the expansion of vertebrates on land

Tetrapod biodiversity today is great; over the past 400 Myr since vertebrates moved onto land, global tetrapod diversity has risen exponentially, punctuated by losses during major extinctions. There are links between the total global diversity of tetrapods and the diversity of their ecological roles, yet no one fully understands the interplay of these two aspects of biodiversity and a numerical analysis of this relationship has not so far been undertaken. Here we show that the global taxonomic and ecological diversity of tetrapods are closely linked. Throughout geological time, patterns of global diversity of tetrapod families show 97 per cent correlation with ecological modes. Global taxonomic and ecological diversity of this group correlates closely with the dominant classes of tetrapods (amphibians in the Palaeozoic, reptiles in the Mesozoic, birds and mammals in the Cenozoic). These groups have driven ecological diversity by expansion and contraction of occupied ecospace, rather than by direct competition within existing ecospace and each group has used ecospace at a greater rate than their predecessors.     

Culture of Clostridium pasteurianum in Defined Medium and Growth as a Function of Sulfate Concentration

Clostridium pasteurianum strain W-5 was selected as an anaerobe which may be grown from large inocula in defined media with sulfate as its primary sulfur source. Since it is important to keep inocula small in minimizing transfer of sulfur sources, culture conditions were optimized. The medium devised decreased lag period and generation time when compared with other media, but growth could not be induced consistently with 6 x 10(6) cells per ml or less. Addition of trace elements, chelating agents, reducing agents, metabolites, and spent medium from various stages of growth did not stimulate growth from small inocula. Generation time was 85 min on inoculation with 10(7) or more cells per ml taken from young stocks, but the lag period decreased somewhat with larger inocula. On the other hand, generation time and lag period increased with age of the inoculum. The total yield of cells increased when buffer capacity was increased. Growth of C. pasteurianum W-5 was dependent upon sulfate at relatively low sulfate concentrations, and the organism is thus suitable for study of sulfur metabolism. No evidence of a maintenance requirement for sulfate was detected.     

Dielectric spectroscopy for noninvasive examination of corneal tissue]

Dielectric spectroscopy is a non-invasive contact technique that permits the in vivo measurement of the specific electrical properties of biological tissue induced by an external electrical field. Permittivity, relaxation time and specific conductivity as a function of corneal hydration (wet weight/dry weight) and temperature were measured in 10 porcine corneas. Variation of tissue hydration has a minor influence on the signal, with a significant variation of the signal being detectable only for relatively dry tissue. A much greater influence was found for temperature, in particular on relaxation times. Dielectric spectroscopy provides us with an opportunity to detect structural, in particular temperature-induced, changes in living tissue. In the frequency range investigated, hydration has only a small influence on the dielectric properties of the tissue.