Arthropod toxins as leads for novel insecticides: an assessment of polyamine amides as glutamate antagonists.

In the search for new toxins, preferably with new sites of action, the polyamine amides represent a new class of compounds with potential as insecticides and as pharmaceutical agents due to their antagonism of ligand-gated cation channels. In particular, they are potent antagonists of the L-glutamate receptors of insect skeletal muscle. In this paper, we report on synthetic studies to produce hybrid analogues based upon the argiotoxin spider toxins and philanthotoxin-433 which is obtained from a solitary, parasitic wasp. We speculate upon possible modes and sites of action for these antagonists and we discuss their potential as insecticides and in the possible treatment of ischaemic damage. The synthesis and characterization of 4-hydroxyphenylpropanoylspermine is reported and the locust muscle biological assay is described. Using this pharmacological screen, structure-activity relationships have been determined in our laboratories. These are reviewed in the light of the current literature. Voltage clamp studies of the synthetic analogue philanthotoxin-343 and the effects of this polyamine amide on glutamate receptors expressed in Xenopus oocytes are outlined. In conclusion, a description of our current ideas and understanding of the many sites and modes of action of the polyamine amides, based both upon our own studies and also upon those recently reported, is presented.

Differential expression of trophoblast lymphocyte cross-reactive (TLX) antigens on T and B lymphocytes.

Heterologous sera raised to human trophoblast (TLX antisera) have been shown to recognize peripheral blood lymphocytes (PBL); in unrelated studies noncytotoxic Fc receptors blocking B lymphocyte antibodies have been found in the sera of women during normal pregnancies. This study aimed to determine whether (a) there was any relation between Fc receptor blocking and cytotoxic anti-TLX activity in ten TLX sera and (b) different reactivity patterns arose when ten TLX antisera were tested in the cytotoxicity assay against separated T and B lymphocytes. Independent factor analysis showed four antisera with T lymphocytotoxicity patterns giving a loading high on one mathematical factor and low on a second. Three sera shared the opposite pattern and three were intermediate. The groups were similar but more discrete than those obtained when PBL were used as targets. Patterns of B lymphocytoxicity were dissimilar from T and both differed from the erythrocyte antibody rosette inhibition activity. Activity did not correlate with the HLA-A, -B, or -DR types carried by the panel cells. These data indicate that TLX antisera contain antibodies directly cytotoxic to antigens differentially expressed on T and B lymphocytes and that noncytotoxic Fc receptor blocking antibodies are not associated with any TLX groupings.

Maternal antibodies to paternal B-lymphocytes in normal and abnormal pregnancy.

Sera were obtained prior to conception and during the first trimester of subsequent pregnancies from 22 women over 27 pregnancies; on 15 occasions these pregnancies ended in spontaneous abortion, whereas the remaining 12 achieved live normal babies. In only one pregnancy ending in abortion could antibodies directed to paternal B-lymphocytes determined by the EA rosette inhibition (EAI) assay be detected in the mother's serum, whereas five of the 12 successful pregnancies were associated with such detectable antibodies. Cytotoxic antibodies were also found in all but one of these EAI-positive pregnancies and no antibody activity was present in sera obtained from five primigravidae. These results indicated that normal, but not abnormal, pregnancies were often associated with blocking antibody formation, suggesting that such antibodies may protect the fetus from abortion. However, the failure to detect antibody activity in sera from first trimester primigravidae argues against a central role for blocking antibody, alone, in the maintenance of outbred pregnancy.

Identification of HLA-linked antigens by pregnancy-associated non-cytotoxic alloantisera.

Non-cytotoxic sera obtained from post-partum primiparous and multiparous women were examined by a rosette inhibition technique for the presence of antibodies mediating blockade of human B lymphocyte Fc receptors. Selective activity was demonstrated against a panel of normal human B lymphocytes and lymphocytes from patients with chronic lymphocytic leukaemia (CLL). A pattern of specific activity was found in sera and in their IgG fractions, which was not accounted for by antibodies directed to known HLA-A, -B or -DR antigens. Several sera were identified with selective activity in this assay. As the results of testing sera in a direct binding assay correlated with those of the EA inhibition assay, and since EA inhibitory activity occurred in F(ab')2 fractions of sera, it is possible that these non-cytotoxic antibodies bind directly to B cell surface antigens. Sera may therefore have been identified which possess antibodies to hitherto undefined HLA antigens.

Evidence that protective Fc-receptor-blocking antibodies in renal transplantation are alloantibodies not autoantibodies.

We have previously shown that the presence in pretransplant recipient sera of Fc receptor blocking antibodies detected by the EA inhibition assay is correlated with improved allograft survival. Twenty-four such sera were assessed for the presence of autoantibodies by the EA inhibition and lymphocytotoxicity assays. No autolymphocytotoxic antibodies were found, and autologous EA inhibition was noted in only one case. EA-inhibiting alloantibodies did occur, and their presence was correlated with improved allograft survival. Sera from 37 dialysis patients were also studied, and neither autologous EA inhibiting nor autologous lymphocytotoxic antibodies were present. Thus Fc receptor blocking alloantibodies that were correlated with improved renal transplant survival were not autoantibodies.