Men and women – when it comes to sex are we really so different that we come from different planets? Or are we more similar? In offering our perspective on gender and sex, we explore learnings from history; the biological and physiological makeup of men and women; what science tells us about men and women’s sexual attitudes, behaviors, and feelings; new information about the development of sex and love for men and women and how sexual drive and desires are similar yet different; the importance and value of men regulating their sex drive; thoughts about the “hot potato” issue between men and women – pornography; and finally how similar men and women are when it comes to the ultimate sexual goal – emotional and sexual satisfaction. These issues are important for sexual health because they help you develop realistic expectations about yourself as a sexual man, your relationship, and how to cooperate and share as an intimate team. Canadian health care mall online

Reflect on the sexual stereotypes about men and women. People believe that women are very complex in terms of sexuality, while men are very simple. Others (those who favor political correctness) believe that there are absolutely no differences between the sexes. Still others suggest that men and women engage in “the war between the sexes,” have for centuries, and always will.

To understand the sexuality of men and women, the optimal model is a multidimensional, integrated, biopsychosocial approach. Sexuality is a lifelong developmental process, grounded in the body, profoundly enriched through psychological growth, and culminating in interpersonal integration. The history of men and women’s sexuality in Western culture (as well as other cultures) demonstrates this developmental process. Traditionally, beliefs centered on understanding biological sexuality. Until about 1500 B.C., human beings did not understand that pregnancy was the result of sexual intercourse. The myths that culture designed to explain the meaning and significance of sex and fertility seem naïve and grandiose from our historical vantage point, but they were honest efforts to comprehend sexuality. The integration of the biological, psychological, and inter-personal aspects of sexuality in a scientific manner is new thinking in the last hundred years.

Learnings From History and Canadian viagra online

Men’s sexual health has a fascinating history. Most of us have limited information about the variety and richness of sexuality in history and in cultures other than our own. We have a myopic (near-sighted) view about the powerful energy of sex in culture. In a macroview of history, human sexuality has experienced its own maturing process from a biological to a biopsychosocial understanding. People struggled for biological understanding sexual impulses, penis, erection, vagina, intercourse for centuries. Spiritual, theological, and religious perspectives and superstitions brought meaning in the absence of verifiable observations of science and medicine. Scientific objective, observable, empirical, tangible, and physical knowledge gradually emerged to help validate, integrate, and offer meaning to the realities of sex.

• restore libido and improve erectile function;
• stimulate male hair growth;
• increase muscle mass and strength;
• increase BMD, potentially reducing the risk of fractures;
• improve energy, mood, and motivation;
• increase hematocrit into the normal adult male range.
•  Viagra Online Australia

In most men with ED, T treatment alone is insufficient to restore complete erectile function and permit satisfactory intercourse. Because spermatogenesis requires high local T concentrations that cannot be achieved by exogenous androgen administration, T replacement therapy does not stimulate sperm production and testis size, nor does it restore fertility. Treatment of infertility in hypogonadal men is usually only possible in men with secondary hypogonadism and gonadotropin deficiency, using gonadotropin or gonadotropin-releasing hormone (GnRH) therapy.

The normal “physiological” range of serum T concentrations in adults is broad and usually established in healthy young men. In young hypogonadal men, T treatment produces beneficial clinical effects when serum T concentrations are increased into this normal range. With increasing age, serum T levels decline gradually and progressively, but the physiological significance of this decline is not clear. Initial studies in older hypogonadal men have also demonstrated some beneficial effects of T treatment that increase serum T levels into the normal range. Therefore, the goal of T treatment of male hypogonadism, irrespective of age, is to restore serum T concentrations to within the normal adult range.
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An important consideration in the clinical use of T therapy is the dose–response effect of T on different target organs. Recent studies suggest that some actions of T demonstrate continuous dose-response effects as T levels are increased from below normal to within and above the physiological range—e.g., muscle mass. In contrast, other T actions exhibit threshold effects—e.g., libido—that are stimulated near maximal levels at relatively low T concentrations. In some patients—e.g., elderly men with severe prostate disease—low-dose T supplementation may be more prudent than full T replacement. Although not demonstrated in clinical trials, low doses of T may be sufficient to induce some beneficial effects such as the stimulation of libido and, to a limited extent, anabolic actions on muscle and bone, while minimizing adverse stimulatory effects on prostate growth.

Males with prepubertal T deficiency usually present as adolescents or young adults with delayed puberty, manifesting varying degrees of eunuchoidism characterized by a small penis, a poorly developed scrotum, small testes (< 5 mL), and prostate, lack of male hair growth (facial, chest, axillary, pubic, perianal, and extremity hair), body habitus characterized by long arms and legs relative to height, poorly developed muscle mass, prepubertal fat distribution; reduced bone mass, high-pitched voice, poor libido (sexual interest and desire) and sexual function, reduced energy, mood alterations and lack of motivation, benign breast enlargement (gynecomastia), failure to produce an ejaculate (aspermia) and initiate spermatogenesis (azoospermia), and a relatively low hematocrit (in the female range).

Therefore, in boys with delayed puberty, the therapeutic goals of T treatment are to promote:

• the development of secondary sexual characteristics, including growth of the penis, the scrotum, and a male hair pattern;
• stimulate the acquisition of peak bone mass, long bone growth, and eventual closure of epiphyses [through the
• aromatization of T to estradiol (E2)] without compromising adult height;
• increase muscle mass and strength and reduce fat mass;
• induce laryngeal enlargement and deepening of the voice;
• stimulate libido and erections;
• improve energy, mood, and motivation;
• increase red-blood-cell production into the normal adult male range.

By stimulating accessory sex glands (seminal vesicles and prostate), T treatment stimulates seminal fluid production and an increase in ejaculate volume, but it does not stimulate sperm production sufficient for induction of fertility. Because the most common cause of delayed puberty is not pathological but rather constitutional, T therapy in boys with delayed puberty is usually intermittent and continued only until spontaneous puberty occurs.

Unless severe, T deficiency in adult males is usually more difficult to diagnose because the clinical manifestations are often subtle and attributable to other causes. T-deficient men usually present with poor sexual performance manifested by reduced libido and erectile dysfunction – viagra in canada (ED) as their major complaints, although T deficiency is not the primary etiology in the majority of men with ED.

• They may also manifest gynecomastia;
• infertility due to impaired sperm production;
• diminished chest, axillary, and pubic hair;
• decreased muscle bulk and strength;
• low BMD that may result in osteopenia or osteoporosis;
• low energy and motivation;
• irritability and a depressed mood;
• a mild hypoproliferative anemia in the normal female range – female viagra australian.

Testis size is usually normal but may be small (< 15 mL) in men with profound reductions in sperm production. Hot flushes may occur in men with a rapid onset of severe androgen deficiency.

]]> http://www.diseasesjournal.com/therapeutic-goals-of-t-treatment.html/feed 0 http://www.diseasesjournal.com/v3-loop-peptides-from-hiv-1-strain-mn-have-different-polyanion-binding-specificities-than-the-dbp-subdomain-1-hbm-peptide.html http://www.diseasesjournal.com/v3-loop-peptides-from-hiv-1-strain-mn-have-different-polyanion-binding-specificities-than-the-dbp-subdomain-1-hbm-peptide.html#comments Wed, 23 Jan 2013 22:28:55 +0000 http://www.diseasesjournal.com/?p=394 The heparin affinities of hbs-wt peptide, the cyclic V3 loop peptide of HIV-1 strain MN, and RANTES were the same when tested in heparin-Sepharose columns, and X4 strains of HIV, PvRII and hbs-wt can be inhibited by the same polyanions, but not chondroitin sulfate. To see if there are differences in the specificity by which the V3 peptides and the hbs-wt peptide bind to heparin, an ELISA based on RANTES binding to BSA-heparin was developed much like the hbs-wt ELISA. The only difference to the hbs-wt ELISA is that RANTES is substituted for the hbs peptide, and detection is through a biotinylated mouse anti-RANTES monoclonal antibody followed by horseradish peroxidase-conjugated streptavidin. The V3 loop peptides and hbs peptides were added at different concentrations to compete with RANTES at a fixed 5 nM. The linear and cyclic V3 loop peptides of strain MN that had significant binding on heparin-Sepharose were able to compete with RANTES binding to BSA-heparin in a dose-dependent manner, but the hbs-wt peptide was not.

The subdomain 1 HBM has a conserved role in the DBP protein family for binding to diverse receptors, but only members of the family that bind to DARC are inhibited by polyanions

Studies by Ranjan and Chitnis have identified a site in PvRII in the C-terminal flanking region to the DBP V3-like peptide, between C4 and C7, that contain residues necessary for DARC binding [27]. This study also showed that the C1-C4 region of the P. knowlesi beta protein, a member of the DBP family that does not bind to DARC, was capable of substituting for the P. vivax C1-C4. Upon closer inspection, the consensus heparin binding motif is well conserved in the DBP family, with great similarity between proteins that bind different receptors. The P. knowlesi alpha and gamma proteins have an identical consensus heparin binding site, but only alpha binds to DARC. To see if the consensus heparin binding motif may play a similar role in the binding proteins of other members of the DBP family, the same three alanine substitutions found in pv22KARA were introduced in our previous report by site directed mutagenesis into the plasmids pHKADR22, pHKBDR22, and pHKGDR22. This yielded the constructs pkalphaKARA, pkbetaKARA, and pkgammaKARA, which contain the K221, R224, and R227 alanine substitution in the P. knowlesi alpha, beta, and gamma genes, respectively. All three of these mutants failed to bind rhesus erythrocytes when expressed in COS-7 cells, whereas the parent vectors bind very well. When binding of rhesus erythrocytes to the wild type plasmids in COS-7 cells was measured in the presence of polyanions, only the DARC binding alpha protein was inhibited in a dose-dependent manner.

The hbs-wt peptide eluted at 0.5 M NaCl (Table 1). The hbs-kara peptide did not bind to the column at all, eluting with the wash buffer. In a subsequent experiment, without the wash step, it eluted with 0.01 M NaCl. The cyclic V3 loop peptide of X4 HIV strain MN also eluted at 0.5 M as did the linear peptide of X4 strain IIIB. Of the linear peptides that are overlapping subunits of the MN cyclic peptide, the peptide containing the consensus heparin binding motif eluted at 1.0 M. This is a stronger interaction than the cyclic full-length V3 peptide. Other V3 peptides based on consensus sequences of subtypes B and EA, or specific strains RF and SF2, eluted at 0.15 M. RANTES eluted at 0.5 M. There was no direct relationship between net charge of the peptides and affinity to heparin, as the cyclic MN peptide with a charge of +7 eluted at a lower NaCl concentration than the linear peptide at a charge of +6. The most neutral net charge in the tested group of peptides was 0 for the hbs-wt, and it eluted at 0.5 M NaCl.

An ELISA based on coating plates with BSA-heparin and determining the binding of the hbs-wt peptide, or hbs-kara as a control, was developed. This assay showed high sensitivity for detecting bound hbs-wt peptide with low background as demonstrated by low signal produced by the hbs-kara control (data not shown). The binding was inhibited at the same NaCl concentrations that eluted the hbs-wt peptide in the heparin-Sepharose column at 0.5 M and above (data not shown). When sulfated polysaccharides were added to the ELISA, they inhibited the binding of the hbs-wt peptide in a dose-dependent manner. The same sulfated polysaccharides found to be inhibitory in the erythrocyte invasion assay and the PvRII region binding assay where inhibitory in the ELISA, with no inhibition from chondroitin sulfate C.

Region II of the P. Vivax DBP is blocked from binding to DARC by the same polyanions that inhibit X4 HIV strains

Within the DBP V3-like peptide is a site that conforms to the consensus heparin binding sequences BBXB and BBBXXB, where B represents a basic amino acid and X represents any amino acid including basic amino acids. Some strains of HIV, such as MN, contain a consensus heparin binding motif in the V3 loop, and many X4 strains can be inhibited from infecting target cells by polyanions which may bind to the V3 loop. Polyanions that have been shown to inhibit HIV infection include pentosan polysulfate, heparin, and the algal-derived sulfated polysaccharides Na-spirulan, Ca-spirulan and Na-hornan (Na-HOR). These polyanions also inhibited the binding of DARC+ erythrocytes to PvRII in a dose-dependent manner. They also block P. knowlesi invasion of DARC+ erythrocytes. Chondroitin sulfate C represents a polyanion with similar charge to heparin, but differs in the conformational placement of those charges. Chondroitin sulfate C does not block PvRII binding to DARC, or P. knowlesi invasion of DARC+ erythrocytes, suggesting that the interaction between PvRII and polyanions is related to conformation as well as charge. The same is true for inhibition of the V3 loop by polyanions.

A peptide based on the consensus heparin binding motif in the DBP V3-like peptide binds to heparin with the same affinity as V3 loop peptides of X4 HIV strains and recapitulates polyanion inhibition of PvRII binding to DARC

A peptide based on the consensus heparin binding motif in the DBP V3-like peptide was designed to test the affinity of this site for heparin and compare it to V3 loop peptides and RANTES. Based on results with an alanine substitution mutant of the consensus heparin binding motif in the DBP V3-like peptide, two peptides were designed; one contains the wild type heparin binding site (hbs-wt), and the other contains the same alanine substitutions as the pv22KARA construct (hbs-kara) found in our previous work to abrogate binding to DARC [16]. The peptides are FITC conjugated at the N-terminus and terminate at the carboxyl end with the DYKDDDDK “flag epitope” sequence for fluorescence or antigenic detection, respectively. They are identical with the exception of the alanine substitutions.

PvDBP peptide BSA-heparin ELISA

Polyvinyl chloride 96-well microtiter plates were coated with 5 μg/ml heparin-albumin (Sigma) in a volume of 100 μl per well in 50 mM Tris-HCl pH 7.5 wash buffer overnight at room temperature. Plates were washed three times with wash buffer and blocked for 2 h at room temperature with 1% BSA in wash buffer at 400 ul per well. For polyanion blocking experiments, WT or mutant DBP polyanion binding site peptides were diluted to 10 μg/ml in a final concentration of polyanions at 0, 0.1, 1, 10, 100, or 1,000 μg/ml in wash buffer and added at 100 μl per well for 2 h. For controls, the DBP peptides were added at 10 μg/ml in 0.01, 0.15, 0.5, 1.0, and 2.0 M NaCl 50 mM Tris HCl pH 7.5 (data not shown). Plates were washed three times with wash buffer. Chicken anti-DYKDDDDK epitope antibody (Aves Labs, OR) at 1:5000 in 1% BSA wash buffer was added at 100 μl per well for 1 h at room temperature. Rabbit anti-chicken horseradish peroxidase antibody (Jackson ImmunoResearch) was added at 1:5000 in 1% BSA wash buffer at 100 μl per well for 1 h at room temperature. Plates were washed three times with wash buffer. The reaction was developed with 100 μl per well of 2% 3,3′,5,5′-tetramethylbenzidine 0.1 M NaOAc containing 0.001% hydrogen peroxide for about 5 min. The reaction was stopped with 100 μl per well of 1 M phosphoric acid. Absorbance measurements were made at 450 nm on a Biotek 133 microtiter plate reader. Percentage inhibition of binding was determined by dividing the absorbance at each polyanion concentration by the absorbance at 0 μg/ml of the polyanion, multiplying by 100 and subtracting this value from 100.

RANTES BSA-heparin ELISA

The same ELISA format used for the PvDBP Peptide-BSA-heparin ELISA described above was used for a competitive ELISA to detect RANTES binding to heparin, and competitors to this binding. Wells were coated with BSA-heparin, blocked with BSA and washed. A volume of 100 μl of 5 nM RANTES in wash buffer supplemented with 0, 0.5, 5, 50, 500 or 5000 nM peptide was added to triplicate wells. After incubation for 1.5 h at room temperature, the plates were washed in wash buffer and 100 μl of biotinylated anti-RANTES monoclonal antibody (R&D Systems) was added at 1:500 in 0.1% BSA wash buffer. After 1 h at room temperature, the plates were washed and 100 μl of streptavidin-horseradish peroxidase (Jackson ImmunoResearch) was added at 1:2000 in 0.1% BSA wash buffer. After 1 h at room temperature, the plates were washed. The reaction was developed as above. Percentage inhibition of binding was determined by dividing the absorbance at each peptide concentration by the absorbance at 0 nM of the peptide, multiplying by 100 and subtracting this value from 100.

Blood was collected in 10% citrate phosphate dextrose (CPD) and stored at 4°C unwashed for up to 4 weeks, or washed in RPMI with malaria supplements and stored in malaria culture medium at 50% hematocrit for up to 2 weeks. The DARC+ human erythrocytes used in the erythrocyte binding assay and the P. knowlesi erythrocyte invasion assay had the phenotype Fy(a-b+) as determined by standard blood banking methods using anti-Fya and anti-Fyb antisera (Gamma Biologicals, Houston, TX). Erythrocytes were washed three times in DMEM (Gibco BRL) and resuspended to a hematocrit of 10% in complete DMEM for the erythrocyte binding assay. Erythrocytes used in the P. knowlesi erythrocyte invasion assay were washed three times and resuspended to a hematocrit of 10% using malaria complete RPMI.
Percoll purification of schizont-infected erythrocytes

Cultures of P. knowlesi at 5-10% infected erythrocytes were washed three times in RPMI with malaria supplements and 10% FBS and brought up to a hematocrit of 10%. A 50% Percoll solution was made by adding 0.45 vol 1× PBS, 0.05 vol 10× PBS and 0.5 vol Percoll (Sigma). Two ml of the washed culture was overlaid on 2 ml of the 50% Percoll solution in a 4 ml polystyrene tube and centrifuged for 20 min at 2100 RPM in a Sorvall centrifuge. The ring of cells at the interface was removed, pooled and washed three time in 1× PBS. The pellet was brought up in malaria culture medium to 2 × 107 cells/ml.

P. Knowlesi erythrocyte invasion assay

Human Duffy Fy(a-b+) erythrocytes were washed in complete malaria medium and 2 × 107 washed cells were added to increasing concentrations of sulfated polysaccharide in malaria culture medium at final volume of 900 μl for 1 h at room temperature. To each tube of sulfate polysaccharide-treated erythrocytes, 100 μl or 2 × 106 schizont-infected erythrocytes was added and placed in a well of a polystyrene 24-well plate (Becton-Dickinson). The cultures were maintained under a blood-gas atmosphere at 38°C for 8 h to allow the infected erythrocytes to rupture and release free merozoites capable of infecting new erythrocytes and developing to ring-stage trophozoites. The culture was centrifuged at 2100 RPM for 3 min and a thin smear was made from the pellet. The thin smear was fixed with methanol and stained with Leukostat Solution B (100 mg Eosin Y+ 300 μl 37% formaldehyde +400 mg sodium phosphate dibasic +500 mg potassium phosphate monobasic, q.s. to 100 ml with dH2O), rinsed, and stained with Leukostat Solution C (47 mg Methylene Blue +44 mpp Azure A +400 mg sodium phosphate dibasic +500 mg potassium phosphate monobasic, q.s to 100 ml with dH2O). The percentage of erythrocytes infected with ring-stage trophozoites per 2000 erythrocytes was determined at 1000×. Percentage inhibition of invastion was determined by dividing the percentage of ring-stage parasites at each polyanion concentration by the percentage of ring-stage parasites at 0 μg/ml of the polyanion, multiplying by 100 and subtracting this value from 100.

Polyanions

Ca-spirulan, Na-spirulan, and Na-hornan (Na-HOR) were kindly provided by Toshimutsu Hayashi, Department of Virology, Toyama Medical and Pharmaceutical University, Sugitani, Toyama, Japan. Heparin, dextran sulfate, and pentosan polysulfide were obtained from Sigma-Aldrich (St. Louis, MO).

Peptide preparation

Peptides based on the wild type (wt) putative polyamine binding site of the PvDBP and a non-binding mutant, pvR22KARA (Figure 1) were obtained from Gene med Synthesis, Inc. (San Francisco, CA). The synthesis included N-terminal fluoresce in conjugation and HULK purification to greater than 80%. Peptides of the V3 loop were obtained from the NHI AIDS Reagent Program (NHI AIDS Reagent Program, Rockville, Md.)

Heparin-sepharose columns

The binding affinity of the PvDBP HBM and V3 loop peptides for heparin was determined by chromatography on a heparin-Sepharose column. Heparin-Sepharose CL-6B beads (Pharmacia Biotech) were swollen in 50 mM Tris-HCl pH 7.5 (column buffer), degassed for 1 h, and 1 ml of slurry was added to a 10 ml column. The column was equilibrated with 10 volumes of column buffer. Peptides were added at 1 mg/ml in 300 μl and allowed to enter the column. The column was washed with 3 ml of column buffer. The peptide was eluted with 3 ml volumes of increasing NaCl concentrations of 0.01, 0.15, 0.5, 1.0 and 2.0 M, and 0.5 ml fractions were collected. The column was regenerated between peptides by adding alternating 3 ml volumes of 0.1 M Tris-HCl, 0.5 M NaCl, pH 8.5 and 0.1 M NaOAc, 0.5 M NaCl, pH 5.0 for three cycles. The column was re-equilibrated with 10 vol. of column buffer before adding the next peptide. Fractions were measured for absorbance at 280 nm on a spectrophotometer.

P. Knowlesi in vitro culture

Whole blood from rhesus macaques was collected in 10% CPD and allowed to separate overnight at 4°C. The erythrocyte phase was washed in RPMI with L-glutamine and supplemented with 25 mM HEPES, 300 μM hypoxanthine, 10 μM thymidine, 1.0 mM sodium pyruvate, and 11 mM glucose. This RPMI with malaria supplements was then used to prepare malaria culture medium by adding to a final concentration of 0.24% sodium bicarbonate and 0.2% Albumax-I (Life Tech, Gibco BRL). Cultures were maintained at a hematocrit of 10% in malaria culture medium under an atmosphere of 5% O2, 5% CO2, balanced N2 (Air Liquide, Houston, TX) at 38°C.

The HIV surface glycoprotein gp120 (SU, gp120) and the Plasmodium vivax Duffy binding protein (PvDBP) bind to chemokine receptors during infection and have a site of amino acid sequence similarity in their binding domains that often includes a heparin binding motif (HBM). Infection by either pathogen has been found to be inhibited by polyanions.

Results

Specific polyanions that inhibit HIV infection and bind to the V3 loop of X4 strains also inhibited DBP-mediated infection of erythrocytes and DBP binding to the Duffy Antigen Receptor for Chemokines (DARC). A peptide including the HBM of PvDBP had similar affinity for heparin as RANTES and V3 loop peptides, and could be specifically inhibited from heparin binding by the same polyanions that inhibit DBP binding to DARC. However, some V3 peptides can competitively inhibit RANTES binding to heparin, but not the PvDBP HBM peptide. Three other members of the DBP family have an HBM sequence that is necessary for erythrocyte binding, however only the protein which binds to DARC, the P. knowlesi alpha protein, is inhibited by heparin from binding to erythrocytes. Heparitinase digestion does not affect the binding of DBP to erythrocytes.

Conclusion

The HBMs of DBPs that bind to DARC have similar heparin binding affinities as some V3 loop peptides and chemokines, are responsible for specific sulfated polysaccharide inhibition of parasite binding and invasion of red blood cells, and are more likely to bind to negative charges on the receptor than cell surface glycosaminoglycans.

Introduction

The human immunodeficiency virus type 1 (HIV-1), the human malaria, Plasmodium vivax, and the monkey malaria, P. knowlesi, have ligands that bind to chemokine receptors and mediate cell invasion. The surface glycoprotein gp120 (SU) of HIV-1 binds to CCR5 and CXCR4 as the major coreceptors for infecting CD4+ T-lymphocytes in vivo, and changes in the amino acid sequence of the V3 loop of gp120 can change viral tropism from CCR5 using (R5) to CXCR4 using (X4) to both (R5X4). The V3 loop region of gp120 also provides a neutralizing epitope, and can bind glycosaminoglycans and other polyanions which inhibit viral infection.

P. vivax uses a Duffy binding protein (PvDBP) to bind the Duffy antigen receptor for chemokines (DARC) and invade human reticulocytes. P. knowlesi has three proteins, the P. knowlesi α, β, and γ proteins which can mediate binding to rhesus erythrocytes, and the P. knowlesi α protein (PkDBP) can bind to human and rhesus DARC. PvDBP, PkDBP, P. knowlesi β, and γ proteins are members of a Duffy Binding Ligand (DBL) family of erythrocyte binding proteins with conserved regions of homology which bind to many receptors. Region II within the family, as defined by conserved cysteine residues, is responsible for erythrocyte binding, and region II of PkDBP has been shown to be inhibited by glycosaminoglycan binding.

In a separate report, we describe an amino acid sequence similarity between subdomain 1 in DBP region II and the V3 loop of HIV strain MN. Within subdomain 1 and this V3 loop are consensus BBXB heparin binding motifs (HBM), where B is a basic amino acid and X is any amino acid. This HBM is conserved in many DBL family members, and we previously found that alanine substitutions at this site in PvDBP and PkDBP abrogated DARC binding. RANTES is a natural ligand of both CCR5 and DARC and can inhibit both HIV and DBP binding to their respective receptors. SDF-1 is a natural ligand for CXCR4, and both RANTES and SDF-1 have HBM and are known to bind sulfated polysaccharides.