Cooperation between Carrier-reactive and Hapten-sensitive Cells <Emphasis Type="Italic">in vitro</Emphasis>

THE mechanism, known as the carrier effect, whereby immunity to one or more determinant groups enhances the response to other determinants on the same multivalent antigen, was first recognized in delayed hypersensitivity to haptens, in which, for an appreciable response, the hapten must be coupled to the same protein carrier for priming and challenge^{1, 2}. Carrier specificity has also been demonstrated in the secondary antibody responses to hapten protein conjugates³. Two alternative hypotheses have been advanced to explain this specificity. The “local environment” hypothesis supposes that the hapten-sensitive cell recognizes both the hapten and the carrier determinants. However, the antihapten antibodies produced do not distinguish details of the carrier molecule and so do not reflect the specificity of the cellular receptor. Furthermore, inert spacer molecules inserted between hapten and carrier do not interfere with carrier specificity in the antibody response³. Reflecting current views on the cooperation between thymus-derived (T) and bone marrow derived (B) lymphocytes in the antibody response to various antigens⁴, the second hypothesis invokes two or more cells, one with receptors directed towards the hapten (hapten-sensitive cell), the others specific for the carrier molecule proper (carrier-reactive cells). Supporting this is the observation that pre-immunization to a particular protein carrier alone could potentiate the primary or secondary antihapten response to a hapten conjugated to that protein⁵. In an adoptive transfer system, moreover, the efficiency of antihapten antibody production by cells primed to a particular hapten-protein conjugate and stimulated with the hapten conjugated on a heterologous protein, is significantly enhanced by the introduction of cells primed to the heterologous carrier alone. Anti-carrier serum antibody does not cause such enhancement⁶. The carrier-reactive cells must therefore cooperate in increasing the efficiency of the hapten-sensitive cells in some way other than by providing humoral anti-carrier antibody. Recent work strongly suggests that carrier reactive cells are thymus-derived^{6, 7}.     

Endemism and ecological islands: the ostracods from Jamaican bromeliads

1. The inhabitants of ecological islands, such as the phytolemata of bromeliad plants, provide an opportunity to examine the genetic patterns resulting from island radiations and draw inferences about modes of speciation.
2. Allozyme electrophoresis, as well as mitochondrial DNA and morphological analyses, were employed to delimit species boundaries and assess the population genetic structure of the ostracods from bromeliads on the island of Jamaica.
3. Nine species from the genus Elpidium were both sexually reproducing and endemic to the island. The other commonly encountered ostracod genus, Candonopsis , was represented by at least two sexually reproducing species.
4. Most Elpidium species showed very restricted distributions, low heterozygosity, and marked gene pool fragmentation, suggesting that population bottlenecks have occurred frequently. Whether founder events played a causal role in the diversification of these ostracods remains uncertain, but bromeliad habitats seem to be a source of high biodiversity, and may represent an ideal setting for extensive allopatric speciation.     

Influence of ultraviolet-B radiation on the drift response of stream invertebrates

1. Recent studies have shown that ultraviolet (UV) radiation (280–400 nm) has increased by ≈ 8% in temperate regions over the past decade, but little effort has been devoted to understanding the ecological effects on temperate ecosystems. This research examined the effects of artificial ultraviolet-B (UVB; 280–320 nm) radiation on the drift response of immature stream insects in laboratory microcosms.
2. Two experiments involved natural populations of stream invertebrates, collected from the Cache la Poudre River (September 1994) and the Arkansas River (October 1995) in Colorado. UVB lamps were turned on from 10.00 to 14.00 h each day, and drifting animals were collected on days 1, 3, 5 and 7 during the exposure period. Levels of artificial UVB used in these experiments were similar to levels that stream organisms experience during clear, mid-day conditions at Fort Collins, Colorado (longitude 105°30'; latitude 40°35').
3. Drift was significantly higher in microcosms exposed to UVB than in controls and was dominated by Baetis sp. (Ephemeroptera: Baetidae), Trichoptera (caddisflies) and Simulium sp. (Diptera: Simuliidae). The increased drift of some stream invertebrates in UVB-exposed streams may be a behavioural response and/or a result of injury.
4. Stream organisms may be particularly sensitive to predicted increases in UV radiation, because streams are generally shallow with clear water. As a result of this potential sensitivity, we recommend that research be directed to understanding the ecological effects of UV radiation on these habitats.