Linkage of chloroquine resistance in Plasmodium berghei to infection of immature erythrocytes of mice.

Studies of infective potency were done to determine why chloroquine-resistant $\text{P.}$$\text{berghei}$ is an obligate parasite of immature erythrocytes. Infective potency was estimated from the length of time required for mice to develop parasitemia of 2% (delay in parasitemia). The delay in parasitemia was an inverse linear function of the logarithm of the number of parasites inoculated. A single regression line fitted the data both for susceptible and for resistant parasites, indicating identical infective potencies which, in turn, indicates that chloroquine-resistant $\text{P.}$$\text{berghei}$ selects and preferentially infects immature erythrocytes whereas it rejects mature erythrocytes.     

Interleukin 2 and concanavalin A stimulate interferon-gamma production in a murine cytolytic T cell clone by different pathways

We identified a variant murine cytolytic T lymphocyte (CTL) clone which, in contrast to the parent clone and all other murine T cell populations tested, was found to have acquired spontaneously the ability to produce interferon-gamma (IFN-gamma) in response to recombinant interleukin 2 (rIL-2). IFN-gamma production in response to concanavalin A (Con A), which was characteristic of all T cell populations tested, was preserved in this variant. The IFN produced by the variant in response to either stimulus was active in both a macrophage-activating factor assay and an anti-viral assay. Both activities induced by either stimulus could be blocked by monoclonal anti-IFN-gamma antibodies. Upon Northern blot analysis using an IFN-gamma-specific cDNA probe, the IFN-gamma RNA isolated from variant cells stimulated with Con A or IL-2 were found to migrate equivalently. The unusual pattern of responsiveness in this variant CTL was exploited to compare the mechanisms involved in induction of IFN-gamma production by Con A or IL-2. Striking differences were observed. Unlike IFN-gamma production induced by Con A, IFN-gamma production induced by IL-2 was not accompanied by an elevation of intracellular Ca2+ levels, did not require physiologic extracellular Ca2+ levels, and was not inhibited by the immunosuppressive agent cyclosporin A. Thus, in this variant CTL clone, conditions that have ordinarily been associated in an obligate manner with lymphokine gene expression were found instead to be related to the specific mode of stimulation.     

Ferriprotoporphyrin IX and cell lysis: a protective role for hydrogen peroxide

Two potentially lytic substances, ferriprotoporphyrin IX (FP) and hydrogen peroxide, may coexist and partially detoxify each other in sickle cells and in erythrocytes infected with malaria parasites. Since hydrogen peroxide can decompose FP, its effect on hemolysis induced by FP and by the complex of FP with chloroquine was investigated. Human erythrocytes suspended at a concentration of 0.5% in a 50 microM solution of FP underwent approximately 42% hemolysis during the course of 2 hours. Twenty-five micromolar chloroquine potentiated hemolysis to 99%, and preincubation of 50 microM FP with 25 microM hydrogen peroxide for 5 minutes reduced hemolysis to 4%. Mixing either FP or hydrogen peroxide first with chloroquine abolished the effect of hydrogen peroxide. Detoxification of FP by hydrogen peroxide may be an important protective mechanism in certain hemolytic anemias, and inhibition of detoxification could account for the effectiveness of chloroquine in malaria.     

Effects of octopamine on miniature excitatory junction potentials from developing and adult moth muscle

Intracellular recordings of excitatory junction potentials (EJPs) and miniature EJPs (MEJPs) were made from the dorsal longitudinal muscle of Manduca sexta to determine the sites of action of octopamine. MEJPs increased in amplitude and frequency as the moth developed during the 3 days before eclosion. DL-Octopamine (5 X 10(-6) M) increased the amplitude of excitatory junction potentials in both immature moths (one day before eclosion) and adults. Octopamine (10(-5) M) also increased the amplitude and frequency of MEJPs from immature animals (one and two days before eclosion) but had the opposite effect on adults and pharate adults ready to eclose. Treatment with octopamine (10(-5) M) resulted in a decrease in input resistance and a hyperpolarization in both immature and adult muscle fibers. The results suggest that octopamine acts both presynaptically and postsynaptically but that the increase in the amplitude of the evoked response is due primarily to influences on presynaptic processes.     

Calculating the expected frequencies of potential secondary structure in nucleic acids as a function of stem length, loop size, base composition and nearest-neighbor frequencies.

A formula is derived to estimate the expected frequency of potential secondary structure of a given stem length and loop size in a random sequence of nucleotides of known length and composition. An example is provided using the SV40 sequence which shows significant non-randomness in stem length but whose significance is reduced by more than six orders of magnitude by taking nearest neighbor frequencies into account.     

A method for estimating the number of invariant amino acid coding positions in a gene using cytochrome c as a model case

This paper shows, within the limitations of the assumption stated below, that approximately 27–29 of the unmutated codons which determine the amino acids of cytochrome c are invariant because of biological requirements. A mutation is defined here as the change of a single base in the sequence of a trinucleotide codon, which change alters the amino acid coded for. Codons, if any, in which mutations would be vigorously selected against are termed invariant codons. We assume that, subject to one adjustment, those mutations in the cytochrome c gene which survived in the descent of today's species are randomly distributed among the variable codons. The one adjustment arises from the possibility that a very few codon positions may exhibit frequencies of mutation sufficiently great to justify the exclusion of these codons from the overall distribution on the grounds that the frequency of mutation occurring in these few positions is clearly inconsistent with the assumption of randomness. There are 5 out of the total 110 codons in the cytochrome c structural gene which have clearly sustained an abnormally large number of mutations.This project received support from grants to W.M.F. from the National Institutes of Health (NB-04565) and the National Science Foundation (GB-4017).     

Two lipocortin-like proteins, endonexin II and anchorin CII, may be alternate splices of the same gene

The annexins are a family of phospholipid- and Ca2+-binding proteins that are structurally related. Two members of this family, human endonexin II and chicken anchorin CII, may arise from the same gene by alternative splicing of two structurally unrelated segments.     

Herpes simplex virus glycoprotein D is recognized as antigen by CD4+ and CD8+ T lymphocytes from infected mice. Characterization of T cell clones

Several previous reports have described the surprising inability to detect murine CTL specific for glycoprotein D (gD), one of the important protective immunogens of HSV. Using slight variations of published procedures, we were able to show that the immune response to HSV in infected mice includes the generation of CTL specific for gD. C3H/OuJ (H-2k) mice were infected by injection in the hind footpads with purified HSV-1. Lymphocytes from draining lymph nodes were then isolated and shown to proliferate in response to, and to kill, transformed fibroblasts (H-2k) expressing HSV-1 gD. Two gD-specific T cell clones were isolated. One clone, designated CGD1, was shwon to be CD8+. This clone recognizes HSV-1 gD, but not HSV-2 gD, in the context of class I MHC molecules and kills the appropriate MHC-matched fibroblasts expressing HSV-1 gD. Unusual features of this cytolytic clone include augmentation by IL-4 of proliferative responses to Ag, inhibition of its lytic activity by a mAb specific for Thy-1 and recognition of infected fibroblasts in preference to infected lymphoblasts. The other clone, designated CGD3, was shown to be CD4+. This clone recognizes both HSV-1 gD and HSV-2 gD in the context of class II MHC molecules and has cytolytic potential.