In Vitro Cytotoxicity and Cytokine Production by Lipid-Substituted Low Molecular Weight Branched PEIs Used for Gene Delivery

Lipid-modified low molecular weight branched polyethyleneimines (PEIs) are promising non-viral gene delivery systems that have been successfully explored for treatment of various diseases. The present study aims to determine in vitro safety of these delivery systems based on assessment of cytotoxicity with peripheral blood mononuclear cells (PBMCs), hemolysis with human red blood cells (RBC) and cytokine secretion from several sources of PBMCs. The viability of cells treated with lipopolymer/pDNA complexes was dependent on the polymer:pDNA ratio used but remained low at therapeutically relevant concentrations for most lipopolymers, except for the propionic acid substituted PEIs. The extent of hemolysis was minimal and below the accepted safety levels with most of the lipopolymers; however, some linoleic acid substituted PEIs yielded significant hemolysis activity. Unlike strong cytokine secretion from PMA/IO stimulated cells, most lipopolymer/pDNA complexes remained non-responsive, showing minimal changes in cytokine secretion (TNF-α, IL-6 and IFN-γ) irrespective of the lipopolymer/pDNA formulations. The 0.6 kDa PEI with lauric acid substituent displayed slight cytokine upregulation, however it remained low relative to the positive controls. This study demonstrated that the lipid modified LMW PEIs are expected to be safe in contact with blood components. However, close attention to lipopolymer concentration and ratio of polymer to pDNA in formulations might be required for individual lipopolymers for optimal safety response in nucleic acid therapies. STATEMENT OF SIGNIFICANCE: : This manuscript investigated the safety aspects of various lipid modified low molecular weight polyethylenimine (LMW-PEI) polymers employed for pDNA delivery through in vitro studies. Using peripheral blood mononuclear cells (PBMCs) from multiple sources, we show that the hemolysis ability was minimal for most polymers, although a particular lipid substituent (linoleic acid) at specific ratios exhibited hemolysis. The levels of pro-inflammatory cytokines (TNF-α, IL-6 and IFN-γ) were slightly upregulated only with a lauric acid substituted 0.6PEI, but remained low relative to positive control treatments. We further report the beneficial effect of polyacrylic acid additives on hemolysis and cytokine secretion to a reasonable extent. This study confirms the feasibility of using LMW-PEI as safe delivery agents for various therapeutic purposes.

Leupaxin Expression Is Dispensable for B Cell Immune Responses

The generation of a potent humoral immune response by B cells relies on the integration of signals induced by the B cell receptor, toll-like receptors and both negative and positive co-receptors. Several reports also suggest that integrin signaling plays an important role in this process. How integrin signaling is regulated in B cells is however still partially understood. Integrin activity and function are controlled by several mechanisms including regulation by molecular adaptors of the paxillin family. In B cells, Leupaxin (Lpxn) is the most expressed member of the family and in vitro studies suggest that it could dampen BCR signaling. Here, we report that Lpxn expression is increased in germinal center B cells compared to naïve B cells. Moreover, Lpxn deficiency leads to decreased B cell differentiation into plasma cells in vitro. However, Lpxn seems dispensable for the generation of a potent B cell immune response in vivo. Altogether our results suggest that Lpxn is dispensable for T-dependent and T-independent B cell immune responses.

Leupaxin is serine phosphorylated and recruited to the immunological synapse upon TCR engagement in cytotoxic T lymphocytes (CTL)

Background

Leupaxin is a member of paxillin family proteins that function as adaptor proteins in integrin signaling. Compared to other members, leupaxin is mainly expressed in leukocytes. However, the role of leupaxin in T cells is unknown.

Results

Leupaxin has been shown to be tyrosine phosphorylated in cells including tumor cells, fibroblasts and B cells. However we detected no leupaxin tyrosine phosphorylation in T cells. Instead, leupaxin showed mobility shift in response to TCR signaling. We demonstrated that the mobility shift was caused by serine phosphorylation and was ERK dependent. Although leupaxin is downstream of integrin receptors, LFA-1 stimulation did not induce leupaxin phosphorylation. Several potentially phosphorylated residues were mutated into alanine individually. When Ser54 was mutated, leupaxin no longer showed mobility shift, suggesting that leupaxin is phosphorylated at Ser54. Leupaxin was recruited to the immunological synapse and colocalized with LFA-1. Leupaxin has N-terminal leucine-aspartic acid (LD) domains and C-terminal LIM domains that contain four double zinc finger motifs. The LIM domains were dispensable for leupaxin localization at the contact zone. Leupaxin failed to be recruited to the immunological synapse after deleting LD2–4 domains, suggesting the importance of LD2–4 domains for the recruitment.

Conclusions

Leupaxin is not tyrosine phosphorylated but serine phosphorylated at Ser54 in response to TCR engagement. Leupaxin is recruited to the immunological synapse through LD2–4 domains. Studies are underway to determine the contribution of leupaxin to CTL adhesion, polarization and degranulation.

Leupaxin Regulates LFA-1 Related Function in Cytotoxic T Lymphocytes (CTL)

Background

Leupaxin is an adaptor protein that functions downstream of integrin receptor engagement. It contains N-terminal LD domains and C-terminal LIM domains. Although leupaxin is primarily expressed in leukocytes, it is very little known about the localization and function in leukocytes.

Results

Degranulation follows the formation of the immunological synapse (IS) and recruitment of MTOC to the IS. Leupaxin co-localizes with MTOC and microtubules, and is recruited to the IS during CTL degranulation. Through deletion of leupaxin domains, it shows that both LD2 and LD4 domains are sufficient for leupaxin recruitment to the IS. Leupaxin fails to be recruited to the IS after deleting LD2–4 domains.

Leupaxin is a focal adhesion protein in adherent cells. Leukocytes do not form classical focal adhesions during migration. We have found that leupaxin is recruited to the contact zone during CTL migration on ICAM-1, and forms very dynamic focal adhesion (FA)-like structures. These structures are assembled in the leading edge, and disappear in the trailing edge. Leupaxin also co-localizes with vinculin and talin at the FA-like structures, which are both FA proteins. Different from the role of leupaxin at the IS, leupaxin C-terminal LIM domain contributes to the localization of leupaxin at the FA-like structures.

Conclusions

Leupaxin localization suggests that it contributes to LFA-1 related processes in CTL, including degranulation and migration, but with different domains. Leupaxin LD domains are necessary for the recruitment to the IS during degranulation, whereas LIM domains are necessary for the formation of FA-like structures during migration.

The tick-derived inhibitor Ixolaris prevents tissue factor signaling on tumor cells

BACKGROUND

Tissue factor (TF) is frequently overexpressed in cancer cells and correlated with more aggressive tumor phenotypes and poor prognosis. In addition to promoting coagulation-dependent metastasis and cancer-associated thrombosis, tumor cell-expressed TF mediates direct cell signaling involving the protease-activated receptor (PAR) 2. Ixolaris is a tick-derived inhibitor of the TF-factor (F)VIIa-Xa coagulation initiation complex which blocks primary tumor growth and angiogenesis in glioblastoma and melanoma models.

METHODS

In this study we address the anti-tumor effects of Ixolaris in TF-VIIa-PAR2 signaling-dependent breast cancer models, a xenograft model of highly aggressive human MDA-MB-231 mfp cells and a syngeneic model of PAR2-deficient and replete PyMT mouse mammary carcinoma cells.

RESULTS

Ixolaris potently inhibited the procoagulant activity of human MDA-MB-231mfp or murine PyMT breast cancer cells. Ixolaris blocked signaling by the ternary TF-FVIIa-FXa complex, and, surprisingly, at higher concentrations also the binary TF-FVIIa complex on MDA-MB-231 cells. We show that Ixolaris interacts with certain residues in the human VIIa protease domain that are involved in PAR2 cleavage. In contrast to human VIIa, Ixolaris was a poor inhibitor of murine TF-FVIIa signaling and did not attenuate PAR2-dependent tumor growth in a syngeneic mouse model of breast cancer progression.

CONCLUSION

These data show that Ixolaris inhibits PAR2 cleavage specifically by human TF signaling complexes and suggest that Ixolaris may block tumor growth of human cell models with ectopic FVIIa expression through inhibition of direct TF-FVIIa-PAR2 signaling as well as its anticoagulant activity.

Paxillin associates with the microtubule cytoskeleton and the immunological synapse of CTL through its LD domains and contributes to microtubule organizing center reorientation (112.24)

The cytoskeletal adaptor protein paxillin localizes to the microtubule organizing center (MTOC) in T cells and upon target cell binding is recruited to the supramolecular activation complex (SMAC). We mapped the region of paxillin that associates with both the MTOC and SMAC to the leucine-aspartic acid (LD) domains and showed that a protein segment containing LD2-4 was sufficient for MTOC and SMAC recruitment. Paxillin localizes to the peripheral area of the SMAC along with LFA-1 suggesting that LFA-1 may contribute to its recruitment. To test this possibility, beads coated with anti-CD3 were used alongside non-antigen bearing target cells, thus physically separating adhesion and TCR signals. Paxillin preferentially localized to sites of integrin engagement rather than to sites of TCR engagement, further suggesting that LFA-1 contributes to paxillin recruitment. These sites of antigen-independent integrin binding were not sufficient to induce MTOC reorientation. Paxillin has been shown to be phosphorylated downstream of ERK, but when we generated a mutation that abolished detectable phosphorylation we found that paxillin still bound to the MTOC and was recruited to the SMAC. Finally, expression of the LD2-4 region of paxillin reduced MTOC reorientation. These studies demonstrate that paxillin is recruited, through its LD domains, to sites of integrin engagement and may contribute to CTL adhesion and subsequent MTOC reorientation required for directional degranulation.

Inhibitory serpins from wheat grain with reactive centers resembling glutamine-rich repeats of prolamin storage proteins. Cloning and characterization of five major molecular forms

Genes encoding proteins of the serpin superfamily are widespread in the plant kingdom, but the properties of very few plant serpins have been studied, and physiological functions have not been elucidated. Six distinct serpins have been identified in grains of hexaploid bread wheat (Triticum aestivum L.) by partial purification and amino acid sequencing. The reactive centers of all but one of the serpins resemble the glutamine-rich repetitive sequences in prolamin storage proteins of wheat grain. Five of the serpins, classified into two protein Z subfamilies, WSZ1 and WSZ2, have been cloned, expressed in Escherichia coli, and purified. Inhibitory specificity toward 17 proteinases of mammalian, plant, and microbial origin was studied. All five serpins were suicide substrate inhibitors of chymotrypsin and cathepsin G. WSZ1a and WSZ1b inhibited at the unusual reactive center P(1)-P(1)' Gln-Gln, and WSZ2b at P(2)-P(1) Leu-Arg-one of two overlapping reactive centers. WSZ1c with P(1)-P(1)' Leu-Gln was the fastest inhibitor of chymotrypsin (k(a) = 1.3 x 10(6) m(-1) s(-1)). WSZ1a was as efficient an inhibitor of chymotrypsin as WSZ2a (k(a) approximately 10(5) m(-1) s(-1)), which has P(1)-P(1)' Leu-Ser-a reactive center common in animal serpins. WSZ2b inhibited plasmin at P(1)-P(1)' Arg-Gln (k(a) approximately 10(3) m(-1) s(-1)). None of the five serpins inhibited Bacillus subtilisin A, Fusarium trypsin, or two subtilisin-like plant serine proteinases, hordolisin from barley green malt and cucumisin D from honeydew melon. Possible functions involving interactions with endogenous or exogenous proteinases adapted to prolamin degradation are discussed.

A physical interaction between the cell death protein Fas and the tyrosine kinase p59fynT

The Fas antigen (Apo1/CD95) is a transmembrane protein belonging to the nerve growth factor receptor family. It is expressed on a variety of cells, including activated T lymphocytes. Ligation of Fas with its natural ligand or with anti-Fas antibodies often results in the apoptotic death of the cell, making Fas an important mediator of down-regulating immune responses. The signal transduction pathways utilized by Fas are currently unknown, although tyrosine kinase activity has recently been strongly implicated. Here, we report that the tyrosine kinase p59fyn physically associates with Fas in Fas-sensitive cells. In addition, we show that activated T lymphocytes from fyn knockout mice exhibit elevated lifespans and reduced apoptosis in vitro compared to their normal counterparts. Furthermore, activated T lymphocytes from the fyn-deficient mice are less sensitive to killing by both anti-Fas antibody and Fas-ligand cytotoxic T cells. These results suggest that p59fyn plays an important role in Fas signal transduction.

Clinical applications of growth hormone for ovarian stimulation

The realization of the existence of an intra-ovarian regulating mechanism involving insulin-like growth factor-I (IGF-I), a mediator of growth hormone (GH) action that augments the ovarian response to gonadotrophins, has prompted a number of clinical trials exploring the use of GH as an adjuvant for ovarian stimulation with human menopausal gonadotrophin. A critical review of these studies pinpoints a select group of infertile patients who may benefit from this co-treatment, particularly those who have a surgical, pathological or medically induced dysfunction of GH kinetics. The mechanism of this action, the effective dose needed and the implications regarding the interface of GH, IGF-I and ovarian physiology and pathology are now becoming clearer. A greater understanding of GH action on the ovary may in future benefit patients afflicted by anovulatory infertility and those requiring ovulation induction for in-vitro fertilization.

Myxoma virus and Shope fibroma virus encode dual-specificity tyrosine/serine phosphatases which are essential for virus viability

Sequence analysis of the genomes of the Leporipoxviruses myxoma virus and Shope fibroma virus (SFV) led to the discovery of open reading frames homologous to the vaccinia H1L gene encoding a soluble protein phosphatase with dual tyrosine/serine specificity. These viral phosphatase genes were subsequently localized to the myxoma BamHI-I fragment and the SFV BamHI-M fragment, and the resulting encoded proteins were designated I1L and M1L, respectively. The localization and orientation of the myxoma I1L and SFV M1L open reading frames within the well conserved central core of the viral genomes closely mirror that of the Orthopoxviruses vaccinia virus and variola virus. The myxoma I1L and SFV M1L phosphatases each contain the conserved tyrosine phosphatase signature sequence motif, (I/V)HCXAGXXR(S/T)G, including the active site cysteine, found previously to be essential for phosphotyrosine dephosphorylation. The vaccinia H1L phosphatase was originally shown to have the ability to dephosphorylate phosphotyrosyl and phosphoseryl residues in vitro. To assess whether this is a common feature of poxvirus phosphatases, myxoma I1L was expressed as a GST-fusion protein, purified, and shown to dephosphorylate substrates containing tyrosine and serine phosphorylated residues, in a similar fashion to vaccinia H1L. A myxoma I1L variant, in which the active site cysteine 110 was mutated to serine, was expressed in a parallel fashion to the wild-type I1L protein and found to be completely deficient in its ability to dephosphorylate both phosphotyrosine and phosphoserine amino acids. In an attempt to ascertain the biological requirement for the myxoma I1L phosphatase, we constructed a recombinant myxoma virus containing a disrupted I1L open reading frame. This I1L mutant virus was able to successfully propagate in tissue culture only in the presence of a wild-type complementing gene, and pure virus clones containing only the disrupted allele were not viable. Thus, we conclude that the myxoma I1L dual specificity phosphatase is an essential factor for virus viability.

The role of treatment with growth hormone in infertile patients

The reality of the interaction of GH and its mediator, IGF-I, with gonadotrophins is now established. The results of these studies and others have obvious implications, both physiologically and clinically. Co-treatment with GH augments the gonadal response to gonadotrophins, and it seems to be of particular value in patients who are poor responders to gonadotrophin treatment and who have pituitary hypofunction induced surgically, idiopathically (hypogonadotrophic hypogonadism) or medically (treatment with GnRH analogues). There is conflicting evidence as to whether the observed effect of GH is exerted directly on the ovary or mediated through IGF-I. Treatment with GH causes a distinct increase in serum IGF-I concentrations, which correlate with, but are always higher than, follicular fluid levels, suggesting that GH stimulates hepatic production of IGF-I and that the effect on the ovary is endocrine. Further research will, hopefully, clearly define the precise therapeutic role of GH in the induction of ovulation, the selection of the most appropriate group of patients to be treated, and the minimum dose of GH needed to sensitize the ovary. Further studies are also needed to explore the action of GH and to define the role of IGF-I in the process of follicular development.

Cotreatment with growth hormone for induction of spermatogenesis in patients with hypogonadotropic hypogonadism

OBJECTIVE

To induce spermatogenesis by cotreatment with growth hormone (GH) and gonadotropin therapy in patients with hypogonadotropic hypogonadism who had failed to respond adequately to conventional treatment.

DESIGN

Cotreatment with GH (4 IU) and human menopausal gonadotropin, 150 IU of follicle-stimulating hormone and 150 IU of luteinizing hormone (LH), three times a week, and human chorionic gonadotropin, 2,500 IU, two times a week for 24 weeks after unsuccessful treatment for 12 weeks with either pulsatile LH-releasing hormone or gonadotropins.

SETTING

Specialist Reproductive Endocrine Unit.

PATIENTS, PARTICIPANTS

Seven patients, four of whom had failed to respond adequately to the conventional treatment.

MAIN OUTCOME MEASURES

Serum testosterone (T), estradiol, and sperm production, testicular and semen volume, and serum insulin-like growth factor-I and inhibin concentrations.

RESULTS

Of the four patients who received cotreatment with GH, three increased T secretion (greater than 11 nmol/L) within a relatively short period of time, two produced adequate amount of sperm (13 and 12 x 10(6)/mL), and one of them impregnated his wife. One patient did not respond.

CONCLUSION

The results offer a new approach to the problem of induction of spermatogenesis in patients who respond poorly to conventional treatment because cotreatment with GH enhanced T secretion and sperm production in a relatively short period of time.

Cotreatment with growth hormone, after pituitary suppression, for ovarian stimulation in in vitro fertilization: a randomized, double-blind, placebo-control trial

OBJECTIVE

To explore the effect of cotreatment with growth hormone (GH) for ovarian stimulation after pituitary suppression.

DESIGN

A randomized, double-blind, placebo-controlled study.

SETTING

Specialist Reproductive Endocrine and In Vitro Fertilization (IVF) Unit.

PATIENTS, PARTICIPANTS

Twenty-five IVF patients who had responded suboptimally in a previous treatment cycle. A subgroup of 18 patients were found to have ultrasound (US) findings of polycystic ovaries (PCO).

MAIN OUTCOME MEASURE

The amount of gonadotropin used, development of follicles greater than or equal to 14 mm, number of oocytes collected, fertilized, cleaved and replaced, serum and follicular fluid (FF) insulin-like growth factor I (IGF-I) concentrations.

RESULTS

Cotreatment with GH was associated with a significant reduction in gonadotropins requirement (P less than 0.05). In patients with US-diagnosed PCO more follicles developed (P less than 0.05), more oocytes were collected (P less than 0.03), fertilized (P less than 0.004), and cleaved (P less than 0.02). A significantly higher FF IGF-I concentrations were found in patients receiving cotreatment with GH compared with those who received placebo (P less than 0.04).

CONCLUSION

We believe that there may be a place for GH treatment in selected IVF cycles after pituitary suppression but what the role of IGF-I should further be investigated.

Regulation of CD45 expression in human leukemia cells

The CD45 antigen cluster identifies a family of transmembrane glycoprotein tyrosine phosphatases (PTPases) present on nearly all hemopoietic cells. Recent studies suggest that CD45 may play a role in the control of receptor mediated blood cell responses, and that expression of the CD45 gene varies during bone marrow cell maturation. However, relatively little is known of the mechanisms controlling CD45 expression and function. Here we show that the induction of granulocyte or monocyte differentiation of HL60 leukemia cells is accompanied by a rapid increase in CD45 antigen expression and CD45 PTPase activity. In contrast, other leukemia cell lines induced for monocyte/macrophage differentiation did not show increased CD45. Immunoprecipitation of radiolabelled CD45 glycoprotein from dimethyl sulphoxide (DMSO) treated HL60 cells indicated that the cells expressed 200 and 180 kD isoforms. Northern blots of steady-state RNA from HL60 cells showed a 4-11-fold increase in CD45 transcripts after DMSO treatment, but no alteration in the half-life of CD45 mRNA. Nuclear transcription assays showed that CD45 expression was controlled at the level of gene transcription. Namalwa Burkitt leukemia cells expressing the heterologous epidermal growth factor (EGF) receptor protein tyrosine kinase were used to assess the specificity of CD45 PTPase activity. Co-clustering of CD45 and the EGF receptor with specific monoclonal antibodies failed to alter the EGF stimulated tyrosine phosphorylation of the EGF receptor. These studies indicate that CD45 increases during myeloid maturation, and the expression of the CD45 gene is controlled at the level of gene transcription. Preliminary studies suggest that CD45 does not alter the protein tyrosine kinase activity of the EGF receptor in intact cells, suggesting substrate specificity in vivo.

Combined growth hormone and gonadotropin treatment for ovulation induction in patients with non-responsive ovaries

Four anovulatory patients who did not respond to large doses of hMG over 18-33 days were co-treated in subsequent cycles with human growth hormone. Treatment with growth hormone markedly raised serum insulin-like growth factor concentrations. Two patients had a dramatic ovarian response within 7 days of co-treatment; two menopausal patients did not respond. This combined therapy may be of practical value for ovulation induction in non-menopausal patients with non-responsive ovaries.

[Medial coxa saltans--a difficult diagnosis]

A case of medial coxa saltans is presented here. This is a very rare condition and very difficult to diagnose, which is illustrated by the case history. Bursography as a diagnostic aid is described and a possible form of operative treatment of the condition is reviewed.

Cloned cytotoxic T lymphocyte target cells fail to induce early activation events in effector cytotoxic T lymphocytes

We have explored further the basis for resistance of cloned cytotoxic T lymphocytes (CTLs) to cell-mediated cytotoxicity. We find that most cloned CTLs recognized as specific target cells by other cloned CTLs used as effector cells fail to activate three early events that may be critical in triggering lysis in the effector CTLs: Ca2+ influx, microtubule organizing center (MTOC) reorientation, and serine esterase release. To the extent that any or all of these events are involved in activation or expression of the lytic pathway in effector CTLs, our results suggest that in addition to being inherently resistant to cytotoxic granule extracts, many CTLs are also unable to induce lytic function in other (effector) CTLs. We have found one CTL clone that can respond to recognizable cloned CTL target cells with at least MTOC reorientation and serine esterase release, although the target CTLs are still not lysed. In this case, the resistance of the target CTL to lysis may be due solely to its resistance to cytoplasmic granule contents.

The role of Ca2+ in activation of mature cytotoxic T lymphocytes for lysis

We carried out a detailed analysis of the requirement for Ca2+ in the lysis of target cells by cloned cytotoxic T lymphocytes (CTL). In direct, antigen-specific lysis we always observed an influx of Ca2+ into the CTL concomitant with target cell binding. However, we never observed an increase in CTL Ca2+ content during lectin-mediated lysis, or nonspecific lysis by phorbol myristate acetate-induced CTL. We found that in all three types of lysis (direct, lectin-mediated lysis, C or phorbol myristate acetate-induced) the requirement for Ca2+ in lysis was dictated by the target cell used; the same CTL can kill one target cell in the absence of detectable Ca2+, and absolutely require Ca2+ for the lysis of another target cell. Target cell killing, when it occurred in the absence of Ca2+, was accompanied by microtubule organizing center reorientation in the CTL, showing that this function is not uniformly Ca2+ dependent. These results provide further evidence that Ca2+ is not always required for activation of the lytic pathway in CTL, although Ca2+ may be absolutely required for other CTL functions such as interleukin production or expression of the interleukin 2 receptor.

The role of Ca2+ in activation of mature cytotoxic T lymphocytes for lysis

We carried out a detailed analysis of the requirement for Ca2+ in the lysis of target cells by cloned cytotoxic T lymphocytes (CTL). In direct, antigen-specific lysis we always observed an influx of Ca2+ into the CTL concomitant with target cell binding. However, we never observed an increase in CTL Ca2+ content during lectin-mediated lysis, or nonspecific lysis by phorbol myristate acetate-induced CTL. We found that in all three types of lysis (direct, lectin-mediated lysis, C or phorbol myristate acetate-induced) the requirement for Ca2+ in lysis was dictated by the target cell used; the same CTL can kill one target cell in the absence of detectable Ca2+, and absolutely require Ca2+ for the lysis of another target cell. Target cell killing, when it occurred in the absence of Ca2+, was accompanied by microtubule organizing center reorientation in the CTL, showing that this function is not uniformly Ca2+ dependent. These results provide further evidence that Ca2+ is not always required for activation of the lytic pathway in CTL, although Ca2+ may be absolutely required for other CTL functions such as interleukin production or expression of the interleukin 2 receptor.

Resistance of cloned cytotoxic T lymphocytes to cell-mediated cytotoxicity

Cloned CTLs show an unusually high resistance to lysis by effector CTLs. Several cloned CTL lines in our laboratories are absolutely refractory to lysis by other cloned CTLs, either (a) directly, (b) in the presence of lectin, or (c) by PMA-induced CTLs. They can be lysed to some extent by primary CTL, although they are less than 5% as sensitive as target cells normally used to assay primary CTL lytic activity. Lysis of cloned CTLs by primary CTL effector cells is not enhanced by the presence of lectin, and cloned T cells are also highly resistant to lysis by primary lymphokine-activated killer cells. Cloned CTLs are highly resistant to lysis by isolated CTL granules that contain the membranolytic pore-forming protein (PFP or perforin), while non-CTL targets are highly susceptible to granule-mediated killing, indicating that cloned CTLs resist lysis not only at the intact effector cell level but also when soluble effector proteins are used. This resistance mechanism may explain how CTLs kill but spare themselves from being killed during the cytolytic event.

Clinical application of the chromogenic assay of factor VIII in haemophilia A, and different variants of von Willebrand's disease

A chromogenic substrate kit for determination of factor VIII activity (COATEST Factor VIII) was compared to a one-stage clotting assay and the correlation was evaluated in different genetic variants of mild and moderate haemophilia A, in severe haemophilia A and in all known variants of von Willebrand's disease. In all these cases a high correlation between the two methods was obtained. A good correlation was also obtained after intranasal administration of DDAVP (1-desamino-8-D-arginine vasopressin) to patients with von Willebrand's disease. The chromogenic substrate method was performed using a microtray technique.

Genetic variation in cultivars of diploid ryegrass,Lolium perenne andL. multiflorum, at five enzyme systems

Samples of approximately 100 plants from each of 22 populations ofLolium perenne representing 15 cultivars, and from 13 populations ofLolium multiflorum representing six cultivars were scored for iso-zyme variants in five enzyme systems, PGI, GOT, ACP, PGM and 6-PGD. From the individual banding patterns a genetic interpretation of the variation was formulated and population studies of the resulting six polymorphic enzyme loci were performed. No strong indications of partial selfing was found since at four of the six loci,Pgi 2, Got 3, Pgm 1 andPgd 1, the genotypic proportions were in correspondence with the Hardy-Weinberg expectations. This indicated, further, that the genetical interpretations of the banding patterns might be correct. Deviations from Hardy-Weinberg proportions forAcp 1 andGot 2 indicated presumably selection working on the linkage group including these loci. Gametic phase disequilibrium was observed betweenPgi 2 andPgd 1 for populations of one cultivar. These results were discussed in relation to the variation expected within a cultivar.