Mechanism delineating differential effect of an antiestrogen, tamoxifen, on the serum LH and FSH in adult male rats.

Tamoxifen, a synthetic non-steroidal antiestrogen with residual estrogenic activity, administered to adult male rats reduces their fertility. A decrease in the circulating LH and testosterone levels with a transient rise or no change in circulating FSH levels was observed. The present study was carried out to delineate the mechanism causing the differential effect of tamoxifen on circulating gonadotropins by correlating it to changes in the hypothalamic LHRH, pituitary gonadotropins and testicular inhibin/activin. Hypothalamus, pituitary-hypothalamus complex (PHC) and intact pituitary (PI) from control and tamoxifen-treated male rats were superfused in vitro, and pulsatile release of LHRH by hypothalamus and that of LH and FSH by the PHC and PI were studied. Concomitantly, testicular immunoexpression of alpha and betaB subunits of inhibin/activin were studied by immunohistochemistry and enzyme-linked immunosorbent assays (ELISA). At 0.4 mg/kg/day dose of tamoxifen a decrease in mean hypothalamic LHRH and LH pulse frequency from PHC construct was observed. FSH pulse frequency was not affected under the same experimental conditions. At the same dose of tamoxifen, testicular expression of both alpha and betaB subunits of inhibin/activin was upregulated. The study demonstrated that reduced circulating LH levels were due to a decrease in hypothalamic LHRH concentration and in LH pulsatility following tamoxifen treatment. The lack of effect on circulating FSH under the same experimental conditions was likely due to its modulation by inhibin and activin.

Aspirin and salicylate inhibit colon cancer medium- and VEGF-induced endothelial tube formation: correlation with suppression of cyclooxygenase-2 expression.

To determine whether aspirin and salicylate suppress colon cancer cell-mediated angiogenesis, we evaluated the effects of aspirin and sodium salicylate on endothelial tube formation on Matrigel. Aspirin and sodium salicylate concentration-dependently inhibited human endothelial cell (EC) tube formation induced by conditioned medium collected from DLD-1, HT-29 or HCT-116 colon cancer cells. Aspirin and sodium salicylate at pharmacological concentrations were equally effective in blocking tube formation. Neutralizing antivascular endothelial growth factor (VEGF) antibodies blocked colon cancer medium-induced tube formation. VEGF receptor 2 but not receptor 1 antibodies inhibited tube formation to a similar extent as anti-VEGF antibodies. These results indicate that VEGF interaction with VEGF receptor 2 is the primary mechanism underlying colon cancer-induced angiogenesis. Aspirin or sodium salicylate inhibited VEGF-induced tube formation in a concentration-dependent manner comparable to that of inhibition of colon cancer medium-induced endothelial tube formation. It has been shown that cyclooxygenase-2 (COX-2) is pivotal in cancer angiogenesis. We found that colon cancer medium-induced COX-2 protein expression in EC and aspirin or sodium salicylate suppressed the cancer-induced COX-2 protein levels at concentrations correlated with those that suppressed endothelial tube formation. Furthermore, aspirin and sodium salicylate inhibited COX-2 expression stimulated by VEGF. These findings indicate that aspirin and other salicylate drugs at pharmacological concentrations inhibit colon cancer-induced angiogenesis which is correlated with COX-2 suppression.

Tamoxifen, protein kinase C and rat sperm mitochondria.

Tamoxifen at a dose of 400 microg/kg/day has been reported to reduce the fertility of adult male rats and alter the pattern of cauda sperm motility from forward progressive to circular yawing type. Since sperm motility is powered by mitochondria, the effect of tamoxifen on mitochondrial function was studied. Tamoxifen treatment significantly increased rhodamine 123 fluorescent dye uptake by sperm mitochondria, reflecting an altered mitochondrial membrane potential. ATP and DAG levels, activities of glycolytic enzymes, creatine kinase and PKC all remained unaffected by tamoxifen. This is also the first report describing the presence of PKC alpha and beta in rat sperm. Morphological and biochemical integrity of sperm membranes was determined by electron microscopy and malondialdehyde levels, which were unaltered after tamoxifen treatment. This study indicates that the altered sperm motility induced by tamoxifen is accompanied by changes in mitochondrial membrane potential, but in the absence of any detectable change in membrane integrity, lipid peroxidation, ATP levels and activities of glycolytic enzymes, creatine kinase and PKC.

Effect of tamoxifen treatment on motility related proteins in rat spermatozoa.

The study was undertaken to identify the effect of tamoxifen on the expression and phosphorylation of motility related proteins in the adult male rats. For this purpose, tamoxifen, at a dose of 0.4 mg/kg/day, was administered per os to the male rats for a period of 60 days. Cauda sperms, epididymal fluid and tissue proteins were extracted and analyzed by electrophoresis. Testicular tissues fixed in paraffin wax were analyzed for changes in the immunoexpression of interstitial tissue estrogen receptor alpha. Phosphorylation pattern of sperm proteins was studied in vitro after incubating with 32P-ATP. The expression of dynein and tubulin in sperms, and estrogen receptors in epididymis were analyzed by immunoblotting. Tamoxifen treatment did not alter the protein profile in the cauda sperms, epididymal fluid and tissues. Endogenous phosphorylation pattern of sperm proteins in vitro was also not affected, though it is possible that 32P incorporation observed in the 66 kDa protein could be estrogen receptor. Expression of sperm dynein, tubulin and epididymal estrogen receptors was unchanged as was the expression of testicular estrogen receptors. It was concluded that tamoxifen administration alters forward motility pattern characteristic of cauda sperm without any demonstrable change in the expression or activation of motility related proteins and the phosphorylation of the sperm estrogen receptors may be involved in the regulation of sperm motility.

Antifertility effects of fluphenazine in adult male rats.

The underlying mechanisms in human infertility associated with hyperprolactinemia have yet to be established. Hyperprolactinemia is a known side-effect of fluphenazine, a broad spectrum, long-acting phenothiazine known to be D2 dopamine receptor antagonist. Dose-related effects of fluphenazine decanoate were ascertained on the fertility of 60-day treated, adult male rats. Significant increase in the serum levels of prolactin and decrease in the levels of LH and FSH were seen at doses of 1-3 mg/kg/day. No effect was evident on the serum testosterone (T) and estradiol. The tissue levels of Inhibins were not affected. The weights of testes, epididymides, seminal vesicles, ventral prostate, adrenal and pituitary glands were not affected. Testicular histology showed sloughing indicating the sensitivity of this parameter to FSH deficiency. Mating occurred within 10 days of cohabitation in the control and 1-2 mg/kg/day treated groups but delayed in the 3 mg/kg/day treated group with a significant effect on potency. Implantation sites, litter size and fertility index were significantly reduced at 2-3 mg/kg/day doses of fluphenazine. No effects however were seen on sperm counts or motility whereas morphological changes were apparent in the acrosome. Chromatin decondensation in vitro was enhanced and sperm chromatin structure assay revealed DNA denaturation. Hypothalamic tyrosine hydroxylase levels were increased in 1-3 mg/kg/day dose range. Hyperprolactinemic males sired fewer pups as compared to controls. Hypothalamic tyrosine hydroxylase was upregulated at all the doses. The antifertility effects of fluphenazine-induced hyperprolactinemia appeared to be unrelated to testosterone (T). In addition, FSH decrease might have affected the intrinsic sperm quality and thereby reduced litter size.

Effect of oral tamoxifen on semen characteristics and serum hormone profile in male bonnet monkeys.

The effects of oral tamoxifen were studied at a dose of 0.4 mg/kg per day, on the serum hormones and semen parameters in adult male bonnet monkeys, for a period of 90 days. Honey was used as vehicle. Monkeys were treated with honey for 30 days, followed by tamoxifen from Day 30-120 (90 days). Thereafter the treatment was withdrawn until Day 150 of schedule. Blood samples were drawn at 12 and 24 clock hours at monthly intervals for the analysis of luteinizing hormone, follicle-stimulating hormone and testosterone. Semen samples were also collected for analysis once a month, from Day 0-150 of exposure. Tamoxifen treatment produced a transient but significant increase in circulating gonadotropins, at Day 90 of treatment schedule, corresponding to 60 days of treatment. Whilst serum testosterone levels were normal throughout treatment period, an increase was observed after 30 days of drug withdrawal. No effect of oral tamoxifen was evident on semen parameters, viz., volume, counts, morphology and motility. However, throughout the exposure period to honey, a significant increase was observed in sperm counts without any effect on testosterone levels. The present study suggests that oral tamoxifen has a transient antiestrogenic effect on the serum hormones and no effect on semen parameters of adult nonhuman primate males. It is concluded that bioefficacy of oral tamoxifen may have been reduced due to hepatic metabolism.

Estrogen receptor, calcium mobilization and rat sperm motility.

Oral treatment with 0.4 mg/kg/day of tamoxifen citrate, an antiestrogen, has been reported to reduce the fertility of adult male rat, presumably through estrogen receptors expressed throughout the male reproductive tract. During the course of these studies, tamoxifen was observed to gradually alter the pattern of sperm motility in the cauda epididymides without reducing sperm counts. Studies were carried out to understand the mechanism involved in tamoxifen induced change in the sperm motility pattern. In order to study the direct effects of tamoxifen on motility, biochemical levels/activities of sperm calcium, cAMP, phosphodiesterase and dynein ATPase, normally implicated in sperm motility were studied In view of the fact that tamoxifen is a ligand of estrogen receptor, estrogen receptor alpha protein and transcript were localized on rat sperm membrane and the effect of tamoxifen studied. The present study demonstrated presence of estrogen receptor protein and mRNA in the rat sperm by immunofluorescence, western blotting and in situ hybridization respectively. Specificity of sperm estrogen receptors was confirmed by conventional binding studies using [3H]-estradiol. There was no effect of tamoxifen treatment on estrogen receptors in rat sperms. Biochemical analysis of the sperms from tamoxifen treated cauda epididymides revealed a significant increase in the levels of calcium and cAMP. A significant reduction was also apparent in the activity of dynein ATPase. Tamoxifen treatment did not alter phosphodiesterase activity. Estrogen receptors could be identified both in the control as well as tamoxifen treated rat sperms. It was concluded that tamoxifen treatment mobilized calcium from the intra- or extra-cellular pools with a concomitant increase in cAMP and presumably activation of PKA (protein kinase A). Tamoxifen altered the pattern of sperm motility through a calcium induced block in the activity of dynein ATPase, presumably through the activation of sperm phosphatase. The putative estrogen receptor mediated signal transduction pathway appears to be directly affected in the tamoxifen treated, sub-motile rat sperm.

Effect of paternal administration of an antiestrogen, tamoxifen on embryo development in rats.

We have earlier reported that oral administration of tamoxifen causes a dose-dependent reduction in the fertility of adult male rats. The decrease in fertility was mainly due to an increase in pre-implantation loss without an effect on fertilizing ability. During the study, an increased incidence of post-implantation loss of conceptuses sired by tamoxifen-treated male rats was observed. A detailed study was undertaken to investigate dose-related changes in pre- and post-implantation loss and the stage(s) of development at which these losses occurred. The present study demonstrates that tamoxifen treatment produced few normal litters as well as significantly increased pre-implantation loss without affecting the rate of fertilization. Also a significant increase in the number of degenerating embryos at the 2-4-cell stage (days 1-2 of gestation), retrieved from the oviduct/uterus of females mated with tamoxifen-treated males was observed. Histology of the resorbed fetuses, in both control and treated groups, showed presence of trophoblast outgrowth indicative of early placenta formation, which normally occurs on days 8-9 of gestation. The present results suggest that pre-implantation loss occurred at the 2-4-cell stage and the post-implantation loss occurred around days 8-9 of gestation, i.e. around midgestation. The possible effects of paternal tamoxifen treatment on embryogenesis may be due to the reduction of androgens or by the blockage of the estrogen receptor by tamoxifen, thereby affecting germ cell maturation during spermatogenesis.

Temporal effect of tamoxifen on cytochrome P450 side chain cleavage gene expression and steroid concentration in adult male rats.

Adult male rats when treated with 0.4 mg tamoxifen (tam)/kg per day for 90 days show reduced circulating testosterone (T) and LH. The present study was designed to have an in depth understanding of tam induced androgen reduction in adult male rats. Adult male rats were orally administered 0.4 mg tam/kg per day for 30, 60 or 90 days and the temporal effects on intratesticular concentrations of pregnenolone (P(5)), progesterone (P(4)), T, 5 alpha-dihydrotestosterone (5 alpha-DHT) and estradiol (E(2)) were estimated. Control group rats were fed saline. Serum hormonal profile of LH, FSH, T and E(2) was also followed on these days. Testicular levels of cytochrome P450 scc mRNA transcripts on 30, 60 and 90 days of treatment with the same dose were quantitated by biplex RT-PCR using beta Actin as internal control followed by analysis using GelPro Analysis software.A significant reduction in intratesticular P(5), P(4), T, 5 alpha-DHT and E(2) was observed from day 30 of treatment. The P450 scc gene expression in the testis was reduced during treatment period from day 60 of treatment. This study demonstrates for the first time that tam reduces testicular pregnenolone biosynthesis through an effect on cholesterol transport and downregulation of P450 scc gene expression. In confirmation of the observed estrogenic effects of tam in this study, it is suggested that E(2) may have a role in cholesterol transport and testicular pregnenolone biosynthesis at the level of cytochrome P450 scc as shown by us.

Antifertility effects of estradiol in adult male rats.

The dose-related effects of estradiol 17-beta at the doses 0.1 pg, 10 microg, 100 microg, 200 microg, 300 microg, 400 microg, 1,000 microg/kg/day were determined on sperm motility, potency, fertility parameters, serum levels of LH, FSH, PRL and testosterone, weights of testes and accessory sex organs, weights of pituitary and adrenal glands. The drug was administered daily via sc route for a period of 60 days. Dose-related effects on fertility parameters of the estradiol-treated male rats were ascertained by allowing them to mate with normal cycling female rats. Estradiol at 0.1 microg/kg/day dose significantly reduced sperm motility with no effects seen on potency or fecundity, serum LH, FSH, PRL or testosterone, weights of testes and accessory sex organs while pituitary weight increased. Estradiol at 10 microg/kg/day dose significantly reduced motility, serum LH, FSH, weights of testes and accessory sex organs, while pituitary weight increased with no effects seen on potency, fecundity, PRL or testosterone. Estradiol at 100-1,000 microg/kg/day dose significantly reduced motility, potency and fecundity, serum LH, FSH and testosterone, weights of testes and accessory sex organs while serum PRL and the weights of pituitary and adrenal glands increased significantly. Histology of the testes revealed disorganization of the cytoarchitecture in the seminiferous tubules, vacuolation, absence of lumen and compartmentalization of spermatogenesis. Estradiol withdrawal, testosterone propionate at 100 pg/kg/day or antiestrogen (tamoxifen citrate) at 400 microg/kg/day prevented the histological changes. It is conduded that estradiol reduces sperm motility even at a low dose. Low doses (<10 microg/kg/ day) appear to maintain whilst high doses (>10 microg/kg/day) reversibly disrupt spermatogenesis. Prevention of disruption by testosterone or antiestrogen indicates crosstalk between androgen and estrogen receptors in Sertoli cells. Loss of potency and fecundity also suggests effects on crosstalk between these receptors in other male reproductive organs.

Effect of tamoxifen on sperm fertilising ability and preimplantation embryo development.

Recent evidences point to a role of estrogens in males. We have earlier reported that tamoxifen, a synthetic non-steroidal antiestrogen, when administered to adult male rats, in the dose range of 0.04-0.4 mg/kg per day, reduced fertility. The reduced fertility was measured in terms of fertility index (a measure of the efficiency of the ovulated ovas to fertilise and implant), fecundity (siring ability) and litter size. The present study was done to investigate whether the reduction in fertility index was due to reduction in fertilising ability or increase in pre-implantation embryo loss. Also a dose related effect of tamoxifen from 0.02 mg to 2 mg/kg per day on the fertility of the male rats was studied. To study the fertilising ability, control and tamoxifen (0.4 mg/kg per day, the most effective dose) treated adult male rats were mated with normal cycling females and the females sacrificed at day 0-4 of gestation. Eggs fertilised/unfertilised were flushed from the oviduct/uterus and the number and types of eggs were noted. The index of fertilisation, a measure of the fertilising ability was determined. The studies demonstrate that the reduction in fertility is not due to decreased fertilising ability but because of the increased pre-implantation embryo loss as evident from an increase in number of abnormal eggs in the treated group with no change in index of fertilisation. A dose related decrease in fertility was observed. The present study suggests that tamoxifen at 0.02-2-mg dose is predominantly estrogenic in males and paternal factor/s sensitive to tamoxifen is involved in embryogenesis.

Acute activation of gp130 gene expression in bone marrow stromal cells by contact with myeloma-derived lymphoblastic cell line ARH77 cell membranes.

Cell-cell contact of myeloma-derived cell lines (MDCL) or fresh myeloma cells with bone marrow stromal cells (BMSC) is known to induce interleukin-6 (IL-6) and matrix metalloproteinase-1 (MMP-1) production by a marrow stromal cell line. To determine if other BMSC transcripts are altered during cell-cell contact between BMSC and tumor cells, we have used cell lines ARH77 and U266 in an in vitro model. Using mRNA differential display and reverse transcriptase-polymerase chain reaction (RT-PCR), it was determined that a total of 141 transcripts were either upregulated or downregulated in the BMSC on contact with cell membrane from cell lines ARH77 and U266. Induction of two of these transcripts, interleukin-6 (IL-6) and gp130 in the BMSC by ARH77 cell membranes was studied in greater detail. Real-time PCR was used to quantitate transcript levels of gp130, IL-6, and 36b4, a housekeeping gene. Cycloheximide (CHX) alone increased both gp130 and IL-6 transcripts in the BMSC. In addition, CHX caused a superinduction of these transcripts in BMSC exposed to ARH77 cell membranes. The induction of gp130 was independent of the increase in IL-6 mRNA. Upregulation of gp130, a component of the membrane receptors for the IL-6 superfamily, can have profound effects on the response of BMSC to the IL-6 superfamily of cytokines.

Effects of tamoxifen metabolites on fertility of male rat.

The effects of chronic oral administration of tamoxifen citrate, at a dose of 0.4 mg/kg/day, were compared to those of subcutaneous (s.c) administration of tamoxifen citrate, 4-hydroxy tamoxifen, N-desmethyl tamoxifen and intermittent oral tamoxifen administration on the fertility of the male rat and its post reversal progeny. The fertility parameters of 120 day-treated male rat sires from all groups and post reversal male F1 progeny of tamoxifen-treated sires were assessed. Chronic tamoxifen treatment via oral or s.c. routes reduced the fertility of the male rat, weights of accessory sex glands, serum luteinizing hormone, and testosterone levels without altering potency or sperm counts. However, antifertility effects of s.c. treatment were comparatively more consistent than those of oral treatment. 4-hydroxy and N-desmethyl tamoxifen failed to produce significant antifertility effects in the male rat. The antifertility effects of intermittent oral treatment were more sustained than those of chronic oral tamoxifen treatment. It is inferred that hepatic metabolism of tamoxifen interferes with its antifertility effects via oral route and that the parameters affected by chronic oral exposure in the male sires are completely reversed in progeny ensuing after an adequate period of drug withdrawal.

Adhesion of B-Cell Chronic Lymphocytic Leukemia Cells to Marrow Stromal Cells is Mediated by α4ß1 but not ß2αL Integrin: MSC also Prevent Apoptosis of B-CLL Cells.

Interactions between MSC and B-CLL cells were investigated to better understand the role of adhesion proteins in the biology of B-CLL. The role of ß1 and ß2 integrins and CD44 in adherence of B-chronic lymphocytic leukemia (CLL) cells to bone marrow stromal cell (MSC) monolayers and the ability of MSC to prevent apoptosis of CLL cells was investigated. Peripheral blood mononuclear cells, from 8 patients with CD5-positive B-CLL, were effectively depleted of CD3-positive cells with an immunomagnetic column. Purity of B-CLL cells, as judged by coexpression of CD19 and CD5 on two-color fluor-ocytometry, was 92±4% (mean±SD) (n = 8). (51)Cr-labelled B-CLL cells, were incubated with isotype murine monoclonal antibodies or blocking MoAb's against the following adhesion proteins: integrins ß1, α4, and αL (chain of LFA-1), CD44 and CD106 (VCAM-1). The B-CLL cell adherence to marrow stromal cell (MSC) monolayers at 2hrs was 29±12% (mean±1SD). MoAb's against CD106, α4, and ß1 caused a significant inhibition of heterotypic adherence in 2/8, 3/8 and 4/8 experiments. Despite universal expression of αL on B-CLL cells, MoAb against αL did not influence adhesion of B-CLL cells in any of the eight experiments. MoAb's against CD44 caused an increase in B-CLL cell adherence to MSC in 1/8 experiments. No correlation between basal adhesion and intensity of α4 expression was noted. The absence of this correlation can be explained by the highly variable expression of α4 on the B-CLL cells from a limited number of patients. Notably, the intensity of α4 and ß1 expression, on the B-CLL cells correlated with the degree of inhibition by anti-α4 and anti-ß1 MoAb. A significant positive correlation was noted between baseline adhesion and intensity of ß1 expression. Thus, α4ß1 and its ligand VCAM-1 are important for adhesion of B-CLL cells to MSC. However, other ligands of α4 and other as yet undescribed adhesion proteins may also play a role in B-CLL cell adhesion to MSC. In addition, when B-CLL cells were cocultured in direct contact with MSC monolayers, the proportion of B-CLL cells undergoing apoptosis decreased significantly.

Poor quality of sperm as it affects repeated early pregnancy loss.

A study was carried out to determine whether males contribute to repeated early pregnancy loss. Semen samples were analyzed from proven-fertile men (n = 51 group I) and from men whose partners presented with early pregnancy loss (>3 first trimester abortions, n = 32 group II). Routine analysis, sperm function tests, and ultrastructural studies of sperms were carried out. Female factor could be identified in 25 (78%) couples, and in 7 (22%) no cause either male or female could be identified and the semen analysis was normal. Percent morphologically normal did not differ significantly between the groups, but increased sperm head abnormalities were seen. The functional tests were all normal except for a significant decrease in the capacity of nuclear chromatin to decondense in vitro. The ultrastructural studies showed defects of chromatin condensation and irregular nuclei with vacuoles. This study points to the loss of chromatin integrity as a possible contributing factor from males to early pregnancy loss.

Effect of 5alpha-dihydrotestosterone implants on the fertility of male rats treated with tamoxifen.

In adult male rats, tamoxifen (TAM) reduces circulating levels of luteinizing hormone (LH) and testosterone (T) with no effect on follicle-stimulating hormone (FSH) and prolactin (PRL). It reduces the male rat's ability to inseminate the female (potency), as well as its siring ability (fecundity). The objective of the present study was to test whether androgen supplementation could reverse all or some of the observed effects of TAM. To obviate the effects of estrogen, the study was designed to evaluate the beneficial or deleterious effect of 5alpha-dihydrotestosterone (DHT), a 5alpha-reduced, nonaromatizable metabolite of T, on the reproductive functions of TAM-treated adult male rats. Adult male rats received either saline or TAM (0.2 or 0.4 mg per day p.o.) for 90 days. A group of TAM-treated rats was implanted with 6 mg DHT from day 50 to day 90. A third group of untreated animals was implanted with 0-, 1-, 3-, or 6-mg DHT implants for 90 days. Mating studies were done to assess the fecundity, potency, and fertility index at the end of the treatment. Weights of testes, pituitary, and accessory sex organs were recorded, and circulating levels of LH, FSH, PRL, T, and 17-beta-estradiol were estimated. DHT did not affect the fecundity or fertility index. TAM reduced fecundity, potency, and the fertility index. DHT implants improved the fertilizing ability of the TAM-treated male rat. This study discusses and reviews the role of T and 17-beta-estradiol in sperm-fertilizing potential in light of these observations.

Contraceptive knowledge, attitude and practices of men in rural Maharashtra.

Since men are the dominant decision makers in India, it is prudent to discover the knowledge, perception, attitudes and contraceptive practices of men to improve their involvement in the reproductive health needs of families. Three thousand and seventy-two married men from a tribal Primary Health Centre (PHC) area in Thane district of Maharashtra State, India were surveyed with special emphasis on investigating the reasons for not accepting male methods. The majority of them not only had no concept of family spacing, but had not even taken any initiative to improve their knowledge or acceptance of condom/ vasectomy. Men who were aware of contraceptive methods had little knowledge of their correct use. Of the men, 53.7% had positive views about their role in family planning while 66.2% of men stressed the need to improve the acceptance of male methods by providing knowledge and information through sources such as radio, television, door-to-door campaigning and interpersonal communications. Thirty per cent emphasized the need to improve the availability and quality of services. This study indicates a pressing need for effective intervention strategies, both at the community and the clinic level, backed with efficient counselling, motivation and provision of services in rural and remote areas.

CD45 partially mediates heterotypic adhesion between murine leukemia/lymphoma cell line L5178Y and marrow stromal cells.

We raised mAbs to whole L5178Y leukemia/lymphoma (LL) cells to identify adhesion proteins involved in adherence between LL cells and marrow stromal cells. One mAb, 4C, and its subclones 4C.1 and 4C.2 inhibited adherence of L5178Y LL cells to MLT. a nontransformed murine marrow stromal cell line. These MoAbs are directed against CD45RA. Control anti-CD45 mAbs and isotype mAbs were non-inhibitory. Other anti-CD45 mAbs, M1/9.3, RA3-3A1/6.1 and RA3-2C2/1 do not compete with mAb 4C.1 for binding to the L5178Y cell surface, but mAb 4C.1 competes for binding of mAb RA3-2C2/1. Effects of mAb 4C on tyrosine-phosphatase activity of CD45 in L5178Y cells are minimal, suggesting direct involvement of CD45 as an adhesion protein.