Mitogenic proteins of pokeweed. II. The differentiation of human peripheral blood B lymphocytes stimulated with purified pokeweed mitogens (Po-2 and Po-6) from pokeweed, Phytolacca octandra.

Purified pokeweed mitogens, Po-2 and Po-3, extracted from Phytolacca octandra, stimulated plasma cell formation in cultures of human peripheral blood lymphocytes. Plasma cell formation did not occur in cultures of purified B cells but was dependent on T-cell help. High T-cell numbers, however, suppressed plasma cell formation in mixed B- and T-cell cultures stimulated with Po-2. T-cell helper function was exerted across a major histocompatibility barrier and was not dependent on T-cell proliferation. Soluble helper factor(s) from activated T cells were not demonstrated. Po-3 was an effective B-cell stimulant only at concentrations between 0.1 and 1.0 micrograms/ml. In contrast, relatively high concentrations of Po-2 (50--100 micrograms/ml) were required to induce B-cell differentiation. More plasma cells were generated in Po-2-stimulated cultures than in Po-3-stimulated cultures and this was thought to reflect the more aggregated state of Po-2.     

Increased Sensitivity of Lymphocytes from Atopic Individuals to Histamine-Induced Suppression

Histamine depressed lymphocyte reactivity to phytohemagglutinin and, to a lesser degree, concanavalin A, when administered simultaneously with mitogen to lymphocyte cultures. Addition of histamine at later times to the cultures appeared to have a slightly enhancing effect on the lymphocyte response. Stimulation of lymphocytes with pokeweed mitogen was in some cases enhanced, even by high concentrations of histamine. Lymphocytes from atopic individuals were more sensitive to the inhibitory effect of histamine than lymphocytes from nonatopic individuals. The sensitivity appeared age-dependent, but within each age group histamine evoked significantly more suppression on lymphocytes from atopic than from nonatopic individuals. The possibility that the altered reactivity of lymphocytes to histamine, which appears to be associated with atopic allergy, is of pathogenic importance, is discussed, and a hypothesis for the development of atopic disease is proposed.     

Predominance of null mutations in ataxia-telangiectasia

Ataxia-telangiectasia (A-T) is an autosomal recessive disorder involving cerebellar degeneration, immunodeficiency, chromosomal instability, radiosensitivity and cancer predisposition. The responsible gene, ATM, was recently identified by positional cloning and found to encode a putative 350 kDa protein with a Pl 3-kinase-like domain, presumably involved in mediating cell cycle arrest in response to radiation-induced DNA damage. The nature and location of A-T mutations should provide insight into the function of the ATM protein and the molecular basis of this pleiotropic disease. Of 44 A-T mutations identified by us to date, 39 (89%) are expected to inactivate the ATM protein by truncating it, by abolishing correct initiation or termination of translation, or by deleting large segments. Additional mutations are four smaller in-frame deletions and insertions, and one substitution of a highly conserved amino acid at the Pl 3-kinase domain. The emerging profile of mutations causing A-T is thus dominated by those expected to completely inactivate the ATM protein. ATM mutations with milder effects may result in phenotypes related, but not identical, to A-T.      

Influences of contralateral nerve and skin stimulation on neurones in the substantia gelatinosa of the rat spinal cord

Stimulation of high threshold A delta and C fibre peripheral afferents inhibits dorsal horn cells on the other side of the spinal cord. The substantia gelatinosa (SG) is an area full of interneurones known to have commissural connections across the spinal cord. The role of SG in this contralateral inhibitory pathway is investigated here. Forty-three SG cells were recorded in the lumbar dorsal horn of decerebrate spinal rats. Their ipsilateral excitatory receptive fields and responses to sciatic nerve stimulation were recorded. Repetitive electrical stimulation was then applied to the contralateral sciatic nerve. Eight (19%) units were excited by such stimulation. A brief tetanus was followed by an increase of ongoing activity lasting 30 s to 10 min. These cells did not, however, have excitatory contralateral fields. A small separate group of 4 cells (9%) were mildly inhibited by heating or pinching the contralateral limb. The significance of contralateral excitation of some SG cells is discussed in the light of the predominantly inhibitory contralateral effect on dorsal horn cells in laminae 4 and 5. It is suggested that some SG cells may be inhibitory interneurones in their effect on deeper cells.     

The laminar organization of dorsal horn cells responding to peripheral C fibre stimulation

Summary Cat dorsal horn was searched for all detectable units that responded to peripheral C fibre input. Fifty-seven such units were examined in detail. They were located in two main areas. One group was in the superficial laminae 1, 2, and possibly dorsal 3 (n = 29), and the other group was much deeper in laminae 5 and 6 (n = 24). Only four units were situated in the region of lamina 4.Differences were found in the responses to C fibre stimulation of these two groups, both in the optimum stimulus and in the timing of responses to repeated stimulation. Superficial units often did not respond to C fibre stimulation unless a train of two or more stimuli (10 ms apart) were applied, but when responses did occur they were usually very even and regular, with precise onset latencies on repeated stimulation. Deep units tended to need only one peripheral C fibre stimulus for excitation, but the responses were irregular with latencies fluctuating with each stimulus. Some superficial and deep units showed a steady increase in latency of the late C response on repeated stimulation. Increases of up to 80 ms after 30 s of stimulation at 1 Hz were observed.The results are discussed in terms of the neuronal connections in the dorsal horn.The work was supported by the Medical Research Council and the National Institutes of HealthM. Fitzgerald is a Medical Research Council Training Fellow     

An evaluation of high resolution chromosome banding of hematologic cells by methotrexate synchronization and thymidine release

Methotrexate-thymidine synchronization increased mitotic yield and the numbers of cells with longer chromosomes when compared with direct and day culture (24 hr) techniques. The longer chromosomes overlapped more than shorter ones, but this adverse effect of cell synchronization was outweighed by the substantial gains from increased band number of metaphase cells. A critical feature of the synchronization technique that determines chromosome length is the period of cell culture following thymidine release. This will depend on cell cycle time. Variable results obtained with the synchronization technique probably occur because the cell cycle time of leukemic cells differs from that of normal hematologic cells and normal lymphocytes. It may also differ between patients and between acute and chronic forms of leukemia.     

Viscoelastic response of intervertebral disks at audiofrequencies

The viscoelastic responses of intervertebral disks taken from the cervical regions of the spinal columns of several adult, male, mongrel dogs have been determined. The results are presented in terms of a mean complex shear compliance,J _d*=J′ _d ?iJ″ _d , for the disk structures when these are subjected to small-amplitude audiofrequency vibrations (25–5000 Hz) while surrounded by normal salt solution, both at room temperatures and at 98·6°F (37.0°C) (in vitro). Values of the general compliance levels decrease with time after sacrifice, and an abrupt transition in the 100-Hz compliance-time curves at 5·5 hours after death is attributed to the completion of rigor mortis (at room temperature). Comparisons of the broad compliance-frequency disk spectra with those of five synthetic polymeric materials, including a silicone rubber, are presented and suggestions for materials suitable to be used in disk prosthesis are made. Such materials must have values of both elastic compliance (J′) and viscous compliance (J″) which are close to the corresponding living disk compliances. A brief discussion of the characteristic sharp resonance dispersions or fine structure observed in the disk spectra is also presented along with suggestions for future measurements. Finally, the idea is advanced that a composite synthetic structure with a stiff, outer ring of low compliance and a very compliant inner core might most satisfactorily mimic the viscoelastic behaviour of a normal intervertebral diskin vivo.