Why do so many lymphocytes respond to major histocompatibility antigens?

A large fraction of T lymphocytes respond to allogeneic cells. Products of the major histocompatibility (H) complex influence the antigenicity of other cell surface components. We propose that lymphocytes responding to cells that differ genetically only at the major H locus recognize not only the major H difference, but also a multitude of other surface components in combination with the major H antigens. The large frequency of lymphocytes responding to allogeneic cells, then, becomes a function of the number of complex antigens they are recognizing on the foreign cells.     

Is Lake Prespa Jeopardizing the Ecosystem of Ancient Lake Ohrid?

Lake Prespa and Lake Ohrid, located in south-eastern Europe, are two lakes of extraordinary ecological value. Although the upstream Lake Prespa has no surface outflow, its waters reach the 160 m lower Lake Ohrid through underground hydraulic connections. Substantial conservation efforts concentrate on oligotrophic downstream Lake Ohrid, which is famous for its large number of endemic and relict species. In this paper, we present a system analytical approach to assess the role of the mesotrophic upstream Lake Prespa in the ongoing eutrophication of Lake Ohrid. Almost the entire outflow from Lake Prespa is found to flow into Lake Ohrid through karst channels. However, 65% of the transported phosphorus is retained within the aquifer. Thanks to this natural filter, Lake Prespa does not pose an immediate threat to Lake Ohrid. However, a potential future four-fold increase of the current phosphorus load from Lake Prespa would lead to a 20% increase (+0.9 mg P m⁻³) in the current phosphorus content of Lake Ohrid, which could jeopardize its fragile ecosystem. While being a potential future danger to Lake Ohrid, Lake Prespa itself is substantially endangered by water losses to irrigation, which have been shown to amplify its eutrophication.     

Conservation of Glycerolated Cultures of Ochromonas danica and O. malhamensis at −10 C

SYNOPSIS. Ochromonas danica in a complex natural growth medium dies at 6–10 C in 4 days; O. malhamensis in ∼2 days. O. danica grown in the medium supplemented with 4.0% glycerol survived at −10±2 C for 35 days, and with 8% glycerol 29 days. O. malhamensis lasted only to 5 days in these media supplemented with 4% glycerol. Ethylene glycol and dimethylsulfoxide were too toxic to be effective. Difficulties in freeze-preservation of certain other phagocytic cells, notably blood granulocytes having comparatively simple flexuous outer membranes, add interest to use of O. danica and O. malhamensis as test organisms for preservation methods, especially in the convenient, inexpensive -10 to -20 C range. Biphasic media with an overlay of distilled water serve for conservation at room temperature. Problems of mutational erosion of these photosynthetic phagotrophs are discussed.     

Mutation induction by rodent liver microsomal metabolities of aflatoxins B1 and G1 in Neurospora crassa.

The mutagenic activities of aflatoxins B1 and G1 were studied in the ad-3 test system of Neurospora crassa by treatment of conidia with aflatoxin and liver homogenate for 2 h. No significant increase in the ad-3 mutation frequency over the spontaneous frequency was observed when either aflatoxin or mammalian liver homogenate was omitted from the test system. The ad-3 mutation frequencies increased to between 29 and 87/10(6) survivors, which is a 73- to 217-fold increase over the average spontaneous ad-3 mutation frequency (0.4/10(6) survivors), after conidia of N. crassa were treated with 0.67 mM aflatoxin B1, hamster liver homogenate, and a NADPH generating system. A 9- to 15-fold increase in the mutation frequency over the spontaneous mutation frequency was found when 0.67 mM of aflatoxin G1 instead of aflatoxin B1 was used in the test system. Treatment of conidia with 0.44 mM aflatoxin B1 mice liver homogenate and a NADPH generating system caused a small, but significant increase in the ad-3 mutation frequencies. No significant increase in the mutation frequency was found when a single sample of human liver homogenate was used in the test system. These studies show that metabolic activation is necessary for the expression of the mutagenic activity of aflatoxins B1 and G1 in N. crassa.