Nature Vol. 280 19 July 1979 193 monoclonal eliminates the possibility that These data lend support to the proposal their nonspecificity is apparent rather than that the immense polymorphism of the Ecology of real, and that the cells are really producing MHC antigens is due to the massive a very large number of different specific selective advantage of heterozygosity: if photosynthesis factors. the combination of one parent's MHC from Peter D. Moore A similar collection of hybridomas antigen and virus does not elicit a response, producing helper factors would be a great the other parent's may (indeed this has Resource partitioning in plants is less well asset. The biochemical elucidation of been shown9). documented than among animals and this helper factors lags well behind that of However, this begs the question of why is not surprising, for the resources on which suppressors. There is now evidence for antigens that fail to elicit an immune plants depend are fewer and adaptations idiotype-bearing, antigen-specific factors response should survive in the population. which could be referred to as partitioning which replace T cell help in the production The answer may lie in the mechanism of are generally more subtle than is the case of antibodies against phosphorylcholine selective recognition. It is now clear that with animals. This is probably why plant (M. Feldman, University College London) some combinations of MHC antigen and ecophysiologists have eagerly grasped the 10 and (T,G)-A--L (ref.6) but the relationship virus cross-react with alloantigens : it is thus opportunities presented by the gradual of such specific factors to nonspecific highly likely that the combination of some exposition of the extent of the C4 and helper factors remains unclear. J.D. viral antigens with self antigens will cross­ crassulacean acid metabolism (CAM) Watson (University of California at react with other self antigens. Since any cell photosynthetic adaptations among plants. Irvine), for example, reported that T cell reacting strongly against self must be It is well established that both of these growth factor(s) from supernatant of eliminated, it follows that cells reacting modifications to the basic C3 Calvin spleen cells treated with concanavalin A against certain combinations of self and photosynthetic system are associated with would act both as a nonspecific growth virus will sometimes be eliminated too. certain ecologically selective advantages in factor and as a nonspecific helper factor in While it is clear that to avoid conditions of high temperature, high light antibody production or the generation of autoimmune reactions T cells with high­ intensity and water stress. This has led to cytotoxic T cells; but if microcultures of ten affinity receptors for self must be many investigations into the or so cells are expanded with the use of the eliminated, it has been suggested that biogeographical significance of the .growth factor, their supernatants are active receptors with weak affinity for self adaptations, mainly by mapping their only on some cells. This experiment, which antigens are the basis for MHC restricted distributions on a continental scale (see is similar to that of Waldmann and recognition 11 • Tentative evidence in Nature 272,400; 1978). Information is now Lefkowitz 7 suggests that 'nonspecific' support of this theory was presented by H. accumulating concerning the ecological growth factors from concanavalin A Wigzell (Uppsala University), who has value of such adaptations in the local supernatants may be mixtures of antigen or used an anti-idiotypic serum raised against composition of plant communities. idiotype-specific factors; it remains to be immune T cells specific for an allogeneic To search for correlations between the seen whether such mixtures include a antigen to extract the T cell receptor for success of one particular type of genuinely nonspecific T cell growth factor. that antigen. He then labelled internally the photosynthetic system and an MHC restriction, which limits T cell allogeneic antigen, the self antigen of the environmental gradient, such as aridity or recognition of viral antigens to infected immune rat and a third-party antigen, and elevation, is not new. In 1974, Mooney, cells bearing the same MHC antigens, can ran them on Sepharose columns to which Troughton and Berry (Carnegie Inst. Ybk. be seen as a special case of antigen the receptor was bound. Three labelled 73, 793; 1974) reported a survey they had specificity applied to T cells. It has now polypeptides from the third-party control conducted along the coastal strips of become clear that, like any other kind of passed straight through the column; two California and Chile, where the climate antigen recognition, MHC restricted chains from the cells of the immunising shifts from a Mediterranean to a desert recognition is subject to cross-reaction. strain were stopped; and one chain from type with decreasing latitude. They found Cross-reactions have been demonstrated the self strain was retarded. in both locations that increasing aridity was in experiments in which allogeneic virus­ Wigzell interprets this as evidence not associated with an increasing proportion of infected cells are killed by cytotoxic cells only for weak binding of alloreactive CAM plants in the flora. Among C3 plants, depicted of alloreactivity by passage receptors to self, but also as evidence that there was a change from evergreen to through the appropriate mouse strain different polypeptides are involved in the drought-deciduous forms, but C4 plants (J.R. Bennink, University of recognition of self MHC and allo- or viral were virtually absent from all stations. Philadelphia). The cross-reaction may not determinants. It is still a matter of disupte They explain this as a consequence of the be reciprocal: for example, b haplotype whether T cell receptors 'see' virus and low temperatures prevailing at the times of cells may kill infected k haplotype targets MHC antigen as a complex, with only water availability. while k cells will not kill infected b targets 8• one receptor for both ('altered self), or More recent work in the cold winter The converse can also occur: certain whether they see the two antigens with deserts of Utah by Caldwell, White, Moore combinations of haplotype and virus can different receptors ('dual recognition') 12• and Camp (Oeco/ogia, Berl. 29,275; 1977) fail to elicit a cytotoxic response even when Attempts to resolve this question at a has also shown that such C4 species as MHC restriction requirements are met. cellular level are all open to doubt: it is A triplex confertifolia fail to achieve many Much of the interest in such failures of probable that only biochemistry can of the advantages normally associated with recognition is of course due to their produce the answer, and Wigzell's the C 4 system when they commence growth possible bearing on susceptibility to disease experiment may be a first step. D in the cool of spring. They may, however, in man. A McMichael (Oxford University) still match the growth of their C 3 reported that human lymphocytes of competitors and gain the advantage of a certain haplotypes will not show MHC­ 1Eichmann, K. Eur. J. lmmun. 5, 511 -51 7 (1975). longer growing season as summer aridity 2Eichmann, K. & Rajewski, K. Eur. J. lmmun. 5, 661-666 restricted killing in association with g97S). sets in. It is difficult, therefore, to explain influenza virus antigens, whereas others Langman. R. Nature 177,517 (1979) . the lack of C species in the Californian and 4Ben-Nevia el al. Eur. J. lmmun. I, 797 (1978). 4 do. Similarly, S. Shaw (US National 5Taniguchi, M. el al. Nature (in the prc,s). Chilean coastal deserts. Institute of Health) reported that some ~Mozes, E. & Haimovich, J. Nature 171, 56-57 (1979). Eickmeier has now published the results HLA haplotypes elicit much stronger anti­ Lefkowitz, I. & Waldmann, H. Immunology 31,915 (1977). of a similar environmental gradient study 8Doherty, P. &Bennink, J .R. J. exp. Med. 149, 150-157 (1979). influenza cytotoxic responses than others. 9~haw, S. & Biddison, W.E. J. exp. Med. 149, 565-575 (1979) from Texas (Photosynthetica 12, 290; 1 Finbcrg, R. Burakoff, S.J. Cantor, H . & Benacerraf,, B. ffoc. natn. A cad. Sci. U.S.A. 75, 5145-5149 (1978). Peter D. Moore is a Senior Lecturer in the Miranda Robertson is an Associate Editor of Janeway, C.A. Wigzcll, H. & Binz, H. Scand. J. /mmun. 5, Department of Plant Sciences, King's College, Nature. 993-1001 (1976). London. 0028-0836/ 79/290193-02$01.00 (S'=::: Macrnillan Journals Ltd 1979 194 Nature Vol. 280 19 July 1979 1978). Of 88 non-herbaceous species found capacity to withstand water stress. the molecular level, in the functioning of the peptides and nucleic acids of which along a 1,300-m elevation gradient, 22 were The greater competitive success of C3 viruses are made. B. Fields (Harvard CAM, three were C4 and the remaining 63 species in higher altitude, more mesic • has now been Medical School) gave an example of what were C3 Ten samples were taken at 150-m conditions in the tropics altitude intervals; density, frequency and demonstrated by Tieszen, Senyimba, can be done, when he described his study of area cover values were used to determine an lmbamba and Troughton (Oecologia, two pairs of genes, represented by the importance value for each species at each Berl. 37, 337; 1979) along an altitudinal RN As S 1and M2 of reoviruses types I and elevation. The main peak in the importance and moisture gradient in Kenya. They have 3. He studied parent viruses and a of CAM species was found to occur at low found that nearly all the grass species of the collection of recombinants (or reassortants) and showed that S1 nucleic altitude, that of C3 species at higher low altitude grasslands in Kenya are of a C3 Some grass tribes, acid specifies the haemagglutinin protein altitudes and the C 4 peak was intermediate photosynthetic type.