Search

Thymectomised, irradiated mice were injected with syngeneic bone-marrow and reconstituted with a chromosomally marked thymus graft. Peripheral-blood cells were cultured for 3 or 4 days and then ' Colcemid ' was added to arrest dividing cells at metaphase. Fixed cells were examined cytologically. Of 73 mitotic figures which could be scored, 65 were of thymic origin. It is suggested that a considerable number of peripheral-blood mononuclear cells may be of thymic origin.

CELLS from a thymus graft are capable of proliferating in response to certain antigenic stimuli but are apparently incapable of producing antibody1, and it has been suggested that these cells, here referred to as reactor cells, have an important role in initiating immune responses2. In a study of this role we posed the question of whether they would continue to respond after heavy doses of antigen.

IN 1967, Tomasi and Kornguth1 described the purification and partial characterization of a basic protein from pig brain which they later2 suggested was a new tissue specific histone. This was a reasonable assumption considering the general properties of the molecule but it would now seem likely that this protein is in fact one of the basic proteins of myelin. It is now reasonably well established that it is the basic proteins extracted from myelin which are responsible for the experimentally induced allergic encephalomyelitis in animals3, and Bauer4 has recently suggested that there is statistical evidence for the homology of the main determinant of the human encephalitogenic protein (residues 112–122)5 and a part of the amino acid sequence of the histone fraction F2A1. The similarity between the amino acid composition of the myelin basic protein and histones has been noted2 and the differences stressed5, but there can be no doubt that they are quite different proteins. Careful examination of the analysis given by Caspary and Field6 of their encephalitogenic protein of human origin and the purified histone fraction F2A17, however, reveals a remarkable similarity. This being so, and because of the importance of the macrophage electrophoretic mobility (MEM)8 test, which may indicate the existence of malignant neoplasia particularly at an early stage of development, and because of the interest in the isolation of the tumour specific basic protein9, we thought it advisable to test the various histone fractions for their effect in this system. The five histones used were highly purified fractions prepared and characterized by methods which have all been described previously10. They were tested as described by Pritchard et al.11 and the results are given in Table 1.

Chiral isothiocyanate reagents suitable for ‘Edman sequencing’ have been synthesised and used to assess the chiral features of individual stages in the Edman method. Using h.p.l.c. analysis of the diastereoisomeric thiohydantions obtained, it has been deduced that the cyclisation and cleavage of thiazolinone step is the likely source of racemisation of the chiral centre derived from the N-terminal amino acid.

Immunobiology of the Macrophage. Edited by David S. Nelson. Pp. xviii+633. (Academic: New York and London, April 1976.) $39; £21.45.

A reaction sequence for the insertion of amino-acid residues into peptides has been developed using N-ethylacetamide and a Gly-Gly derivative as models.

INTERSPECIFIC hybridization in the genus Lathyrus has been attempted by several workers with little success. Barker1 obtained viable, partially fertile hybrids from the cross L. hirsutus × L. odoratus. Taylor2 claimed to have produced seeds by crossing L. odoratus with L. pratensis reciprocally. It has not been possible to repeat this cross. Senn3 reported failure in 458 attempts at intercrossing seventeen species of Lathyrus and Pisum sativum. Marsden-Jones4 successfully crossed L. rotundifolius with L. tuberosus. In this Department viable seeds have been produced from the following crosses: L. cicera × L. sativus (Saw Lwin*), L. clymenum × L. ochrus (Saw Lwin*), L. clymenum × L. articulatus—reciprocally (Davies), L. articulatus × L. ochrus (Davies), L. hirsutus × L. odoratus (McWhirter*), L. odoratus × L. hirsutus (Davies), L. sylvestris × L. latifolius (Ellis*).

Treatment of 2-cyanomethyl-2′,4′-dimethoxybenzophenone with sodium methoxide in dimethyl sulphoxide gave 9-cyano-2-methoxyanthracen-10-ol in 95% yield. This was oxidised to 2-methoxyanthraquinone in almost quantitative yield, under mild conditions. The relevance of this synthesis of anthraquinones to possible pathways of biosynthesis has been discussed. The interaction of 2-cyanomethyl-2′,4′-dimethoxybenzophenone and sodium methoxide in methanol gave 3-methoxy-1-(2,4-dimethoxyphenyl)isoquinoline.

Monamycin, a crystalline antibacterial preparation isolated from cultures of Streptomyces jamaicensis, consists of a mixture of fifteen cyclohexadepsipeptides, six of which contain chlorine. Each molecular species consists of one residue of α-hydroxy-acid (either L-2-hydroxy-3-methylbutanoic acid or L-2-hydroxy-3-methylpentanoic acid) and five residues of α-amino-or imino-acid. The latter consist of N-methyl-D-leucine, L-proline (or trans-4-methyl L-proline), D-isoleucine (or D-valine), (3R)-piperazic acid [or (3R,5S)-5-chloropiperazic acid, or (3R)-4,5 (or 5,6)-dehydropiperazic acid], and (3S,5S)-5-hydroxypiperazic acid. The name piperazic acid is assigned to hexahydropyridazine-3-carboxylic acid.

EXPERIMENTS carried out on cytologically marked normal F1 recipients implanted with a thymus from a newborn donor of the parental type have shown that cellular traffic from the host to the thymus graft can take place1. Using neonatally thymectomized2–4 or thymectomized and irradiated5 recipients it has been possible to show that cells can also migrate from a thymus graft to the peripheral lymphoid tissue and that these may respond mitotically to immunological challenge6,7. In the situations in which thymic repopulation has been investigated in detail, it has always been possible for cells of thymic origin to react against some of the antigens of the F1 host. It is possible that this antigenic difference between the host and thymus graft might affect the repopulation process. In order to investigate this problem CBA/H recipients and cytologically marked CBA/H-T6T6 thymus graft donors have been used. There is no difference between these strains at the histocompatibility loci3. The cytological constitution of (a) the thymus graft at various times after grafting, (b) the spleen 30 days after thymus grafting and (c) the spleen following injection of antigen at 30 days has been determined.

THYMECTOMY in the new-born1,2 or in the adult irradiated mouse3 leads to a long-lasting suppression of the ability to respond to primary antigenic challenge. It has been shown in both instances that thymus grafting is effective in restoring immunological competence2,4,5 and, furthermore, when using a cytologically marked thymic graft, it has been possible to detect cells derived from the graft in the spleen and lymph nodes2,5. It has, therefore, been suggested5 that it may be these donor cells which are directly responsible for the recovery of the primary immune response in thymus-grafted animals.

D-Isoleucine has been isolated from a natural peptide, the antibiotic monamycin, for the first time.

Thymidine Metabolism and Cell Kinetics By J. E. Cleaver. (North-Holland Research Monographs: Frontiers of Biology. Vol. 6.) Pp. 259. (Amsterdam: North-Holland Publishing Company, 1967.) 86s.