690 Nature Vol. 294 24/31 December 1981 Finally, whatofTRF4? Aftermanyyears functions early (proliferative phase). The given by a current report describing a start of difficulty, created in part by the ability relationship to the newly described B cell on molecular biological studies of IL2. of factors like IL2 and the B cell growth growth factor awaits further experiments. Given several T cell tumour lines which can factor to replace T cells indirectly, assays In both cases, a clearer understanding of be induced to generate high levels of IL2 which clearly distinguish between IL2 and the roles of several lymphokines now (several thousand times the amounts pro­ TRF are now in hand. And the take-home exists, and perhaps more important, the duced by normal lymphocytes), it has been message is that, indeed, TRF exists12 • It tools and approaches necessary for more possible to follow the lead of workers in the acts at the time when B cells, having sophisticated analysis are evident. interferon field, by looking for mRNA undergone clonal expansion following An indication of future directions is coding for the lymphokine, and then antigenic stimulation, are to begin attempting to clone its complementary secreting high levels of immunoglobulin. I. OiSabato, G .• Chen, 0.-M. & Erickson . .1.W. Cell. DNA. The EL4 variant cell line originally Then, as proposed years ago by Dutton and lmmun. 17,495 (1975). described by Farrar and colleagues at 2. Gillis. S. & Smith, K.A. Nature 268, 154 (1977). 13 colleagues, TRF can replace T cells in ). Ruscetti, F.W., Morgan, D.A. & Gallo, R.C. J. lmmun. NIH does indeed contain demonstrable switching on a high level of 119, Ill (1977). IL2 mRNA. The poly (A)+, I l-12S RNA 4. Schimpl, A. & Wecker, E. Nature new Biol. 237. I 5 immunoglobulin synthesis. Using spleen (1972). derived from PMA-stimulated cells of this cells thoroughly depleted of T cells (this 5. Mizel, S.B. & Mize\, D. J. lmmun. 126,834 (1981). line, injected into Xenopus laevis oocytes, 6. Hape!, A.J .• Lee. J.C., Farrar, W.L. & Ihle. J.N. Ce//25, requires treatment of the donor animal 179 (1981 ). directs the synthesis of biologically active 14 with anti-thymocyte serum, in addition to 7. Farrar, J .J .• Mize!, S.8 .. Fullcr-r:arrar. J .• f-'arrar. W .I.. & IL2 • Similar results have been obtained the more common treatment with anti­ Hilfiker, M.L. J. /mmun. 125. 793 (1980). by Gillis and colleagues in Seattle. The next 8. Shaw, J. eta/. J. /mmun. 124, 2231 (1980). Thy-1 antibody in vitro), Swain and co­ 9. Lipsick, J.S. & Kaplan, N.O. Proc. narn. Acad. Sci. phase of work clearly will involve workers have demonstrated synergy U.S.A. 78, 2398 (1981). molecular biological approaches. With IO. l·ord, R.J. eta/. Nature 294,261 (1981). between IL2 and TRF in generating 11. l·arrar, .1 . .1. lmmun. Rel'. (in the press). venture capital panting for release, one plaque-forming B cells. The role of IL2, 12. Swain, S.L, Dennen, G., Warner, J.I·. & Dutton. R.W may also expect that the term 'growth Proc. natn. Acad. Sci. U.S.A. 78. 2517 (1981). although not yet delineated in this system, 13. l'arrar, J..I. eta/. J. lmmun. 125, 2555 (1980). industry' could soon apply to may be related to its ability to induce T cell 14. Blcacklcy, R.C. eta/. J. lmmun. (in th<: press). lymphokinology in more th311 one way. D A new view of supernova remnants in the l\:fagellanic Clouds from David Clark FEw areas of astrophysics have not seen and was used to detect remnants in the emission. The new detections allow the major changes following the highly Magellanic Clouds and other nearby supernova rate in the LMC to be lowered to successful Einstein X-ray observatory galaxies. perhaps one per century, contrasting with mission. The impact on the study of super­ The pioneering survey of SNRs in the earlier estimates of one per 400-900 years. nova remnants (SNRs) has been particu­ Magellanic Clouds by Mathewson and But most significant, the major population larly impressive. When a massive star dies Clarke in Australia in 1973 used the of LMC SNRs now identified in X rays and as a supernova, a shock wave is driven out­ radio/optical technique described above. optically are found to be radio 'sub­ wards from the site of the explosion, The survey identified 14 remnants in the luminous'; this result must call into sweeping-up and heating interstellar gas to Large Magellanic Cloud (LMC) and 3 in question many of the studies of remnant the millions of degrees required for thermal the Small Magellanic Cloud (SMC), and evolution, distribution, ages, birth rates, X-ray emission - so forming an extended was assumed to be almost complete distances and so on in our own Galaxy since X-ray remnant with characteristic (although a few other ring-like nebulosities such studies are based almost entirely on peripheral brightening. Gas cooling behind seen in a deep optical survey of the Clouds radio data. The new uniform LMC sample the shock may be seen to radiate optically, by Davies and co-workers in 1976 were of SNRs should prove invaluble in future and SNRs may also be detected at radio proposed as possible remnants). That studies of remnant evolution at all wavelengths. The radio emission is non­ assumption has been shattered by the wavelengths. thermal, produced by fast electrons X-ray survey of the LMC completed by Observations of the six brightest LMC trapped in the interstellar magnetic field Einstein and recently reported by Long, remnants using the solid-state spectrometer compressed by the expanding shock wave. Helfand and Grabelsky (Astrophys J. 248, on Einstein are to be published shortly. Because X-ray astronomy is a compara­ 925; 1981). Einstein detected X-ray These too show unexpected results. Four of tively young science, pioneering surveys of emission from 13 of the known 14 LMC the six display characteristic thermal SNRs in our own Milky Way, and its remnants, plus 12 other objects which are spectra expected for shock-heated closest galactic neighbours, the Magellanic certain SNRs (5 of which were also in the interstellar material; but the other two Clouds, were carried out in the radio and Davies et al. list), plus 25 further objects show non-thermal spectra suggestive of optical. Within the Galaxy more than 120 which are possible SNRs on the basis of continued energy input. This is the case for extended non-thermal radio objects were existing X-ray data. the well known SNR the Crab Nebula, identified as SNRs. Detectable optical The implications of these new dis­ which in addition to emitting non-thermal nebulosity was found only in the 30 closest coveries are very significant. They seriously X rays is brightest at its centre rather than of these because of the obscuring effect of question the sole use in extragalactic SNR peripherally, the emission being driven by dust permeating the plane of the Galaxy. A surveys of the traditional radio/optical an active pulsar. One of the LMC common characteristic of the optical SNR detection technique as it revealed remnants, going by the rather remnants was recognized - the intensity of perhaps just one-quarter of the LMC unspectacular name of N157B, also shows the red line emission associated with singly population of remnants. Optical unusual central brightening (as Australian ionized sulphur with respect to the intensity nebulosity associated with many of the new radioastronomers showed several years of the red hydrogen Balmer line was very remnants showed sometimes no sulphur ago) and mimics the Crab Nebula in other much greater in the shock-ionized plasma emission - sometimes no hydrogen ways, including the non-thermal X-ray of SNRs than in photo-ionized nebulae. emission. It is the first Crab-like remnant The combination of non-thermal radio David Clark is in the Space and Astrophysics detected in another galaxy, and must Division at the Rutherford Appleton emission and strong sulphur emission was Laboratory, Chilton, Didcot, Oxfordshire represent a prime site for the detection of taken to be a unique signature of SNRs, OXJJ OQX. the first extragalactic pulsar. D 0028-0836/81 /520690-01$01.00 (f') IQR I M~cmillan Journals Ltd .