Assessment of the severity of curly toe.

BACKGROUND: Curly/underlapping toe involves flexion, adduction, and varus deformity of the interphalangeal joints. There are no previous reports showing the relationship between physical examination and X-ray findings among patients with curly toe deformity. METHODS: We investigated the clinical findings of 116 consecutive patients associated with 239 underlapping toes. We compared the age and affected toes between patients whose deformities were pointed out at a pediatric medical examination (group 1) and those referred for medical treatment (group 2). The degree of curly toe deformity was graded by a physical examination and X-ray. RESULTS: The average age at presentation was 2.7 years. The affected toes were significantly different between groups 1 and 2 (p < .001). The morbidity of each toe differed significantly in group 2 (p < .005) but not in group 1. The correlation between the appearance grading and classification by X-ray was very strong using Spearman's rank correlation coefficient. The severity of curly toe was divided into mild in 104 toes, moderate in 105 toes, and severe in 17 toes. The methods of conservative treatment were observation only in 15 cases, manipulations in 30 cases, taping in 67 cases, and a brace in 9 cases. Surgery was performed in 8% of cases. CONCLUSION: Curly toe deformity of the third or fourth toes tend to be referred for medical treatment because of the abnormality. Our grading system using a physical examination and classification by X-ray was useful for assessing the severity of curly toe.

Differences in subtrochanteric and diaphyseal atypical femoral fractures in a super-aging prefectural area: YamaCAFe Study.

INTRODUCTION: Atypical femoral fractures (AFFs) have been correlated with long-term use of bisphosphonates (BPs), glucocorticoids (GCs), and femoral geometry. We investigated the incidence and characteristics of subtrochanteric (ST) and diaphyseal (DP) AFFs in all institutes in a super-aging prefectural area. MATERIALS AND METHODS: We performed a blinded analysis of radiographic data in 87 patients with 98 AFFs in all institutes in Yamagata prefectural area from 2009 to 2014. Among the 98 AFFs, 57 AFFs comprising 11 ST fractures in 9 patients and 46 DP fractures in 41 patients with adequate medical records and X-rays were surveyed for time to bone healing and geometry. RESULTS: Of the 87 patients, 67 received BPs/denosumab (77%) and 10 received GCs (11%). Surgery was performed in 94 AFFs. Among 4 AFFs with conservative therapy, 3 required additional surgery. In univariate regression analyses for ST group versus DP group, male-to-female ratio was 2/7 versus 1/40, mean age at fracture was 58.2 (37-75) versus 78 (60-89) years, rheumatic diseases affected 55.5% (5/9) versus 4.9% (2/41), femoral lateral bowing angle was 1.7 (0-6) versus 11.8 (0.8-24)°, GC usage was 67% (6/9) versus 4.9% (2/41), and bone healing time was 12.1 (6-20) versus 8.1 (3-38) months (p < 0.05). In multivariate analyses, higher male-to-female ratio, younger age, greater proportion affected by rheumatic diseases, and higher GC usage remained significant (p < 0.05). CONCLUSIONS: The incidence of AFFs in our prefectural area was 1.43 cases/100,000 persons/year. This study suggests that the onset of ST AFFs have greater correlation with the worse bone quality, vice versa, the onset of DP AFFs correlated with the bone geometry. The developmental mechanisms of AFFs may differ significantly between ST and DP fractures.

Long-term follow-up for the atypical radial longitudinal deficiency: A case report.

We experienced an atypical case of radial longitudinal deficiency that did not fit into any classifications, including Blauth. The patient had a bilateral hypoplastic thumb, in which the index and middle fingers were missing in the right hand. We performed surgeries in four stages: centralization of the right hand, opponensplasty of the right thumb, opponensplasty of the left thumb, and distraction lengthening of the right ulnar. Twenty-five years after the initial treatment, the patient was satisfied with the treatment and had no significant difficulty with activities of daily living.

The Effect of Elbow and Forearm Position on the Resisted Wrist Extension Test and Incidence of Sensory Disturbance of the Superficial Radial Nerve in Patients with Lateral Epicondylitis.

Background: The aim of this study is to determine the effect of elbow and forearm position on the resisted wrist extension test (RWET) in patients with lateral epicondylitis. We also looked at the incidence of associated sensory disturbance of the superficial radial nerve (SRN) and the effect of treatment of lateral epicondylitis on sensory disturbance. Methods: Sixty-three consecutive patients (68 limbs) with lateral epicondylitis and an equal number of age and gender matched volunteers were investigated. Patients with lateral epicondylitis were subdivided into two groups based on history of corticosteroid injection. We performed the RWET in four limb positions namely elbow extended and forearm pronated (EP), elbow flexed and forearm pronated (FP), elbow extended and forearm supinated (ES), elbow flexed and forearm supinated (FS). Sensory disturbance in the SRN was assessed using a Wartenberg pin wheel. Results: The positivity rate of the RWET was significantly higher in the EP position (100%) compared to the FP (66%), ES (62%) and the FS (24%) positions in limbs with lateral epicondylitis. The RWET was positive only in one subject in the EP position in the control group (1.5%). Sensory disturbance in the SRN territory was present in 63.2% of limbs and only two subjects (2.9%) in the control group. The incidence of sensory disturbance was significantly higher (74.5% vs. 48.3%, p < 0.05) in patients who did not have a corticosteroid injection. Conclusions: The sensitivity and specificity of the RWET is better when it is performed with the elbow in extension with the forearm pronated (EP); 63.2% of limbs with lateral epicondylitis were noted to have an associated sensory disturbance of the SRN and a corticosteroid injection seems to decrease the incidence of sensory disturbances. Level of Evidence: Level II (Diagnostic).

Combining Cylindrical Bone Graft and Headless Screw Fixation for Nonunion of the Medial Trochlea of the Elbow: A Case Report.

CASE: A 19-year-old handballer presented with elbow pain and nonunion of the medial trochlea of the elbow. He had undergone earlier surgery for an elbow injury at 6 years of age. Revision surgery for nonunion was performed using an extra-articular method combining cylindrical bone graft and headless screw fixation. Partial union was observed, and he resumed sports after 3 months, with his limb largely pain-free and functional. At the 21-month follow-up, bone healing was complete. CONCLUSIONS: Combining cylindrical bone graft and headless screw fixation using the extra-articular technique is an option for managing nonunion of the medial trochlea of the elbow.

Midterm results of endoscopically assisted first rib resection in the zero position for thoracic outlet syndrome.

OBJECTIVES: We have hypothesized that an endoscopically assisted transaxillary approach in the zero position would be able to improve visualization and allow safe surgery for thoracic outlet syndrome. METHODS: We performed surgery only for patients with certain objective findings, including blood flow disruption, low blood flow and accelerated blood flow in the subclavian artery demonstrated using Doppler sonography, narrowing of the scalene interval width between the anterior and middle interscalene muscles (interscalene base) or costoclavicular space demonstrated using Duplex ultrasonography or computed tomography angiography. The present study included 45 consecutive patients (50 limbs) who underwent endoscopic transaxillary first rib resection with scalenotomy and brachial plexus neurolysis. We assessed the intraoperative parameters, including the interscalene base, blood loss, operation time, patient satisfaction, preoperative and postoperative Quick Disability of the Arm, Shoulder and Hand and complications. RESULTS: The mean intraoperatively measured interscalene base width was 6.4 mm. All patients showed improvement after surgery. The outcome was excellent in 40% of cases, good in 48%, fair in 12% and poor in none. Pneumothorax was present in 6%. There were no other complications and no recurrences. Among patients who had been followed up for at least 2 years, the Quick Disability of the Arm, Shoulder and Hand score was significantly improved (42 before surgery vs 12 at final follow-up), especially in athletes relative to non-athletes (0.2 vs 16). The present approach achieved complete relief in 43% of cases overall (91% in athletes and 16% in non-athletes). CONCLUSIONS: Endoscopically assisted transaxillary first rib resection and brachial plexus neurolysis in the zero position are useful and safe for thoracic outlet syndrome, especially in athletes.

Progression of Bone and Joint Destruction During the Perinatal Period in Patients With Rheumatoid Arthritis and Juvenile Idiopathic Arthritis in the Last Decade.

BACKGROUND: Rheumatoid arthritis (RA) is a disease that can cause joint destruction and multiple arthritis. We retrospectively investigated bone and joint destruction during the perinatal period in adult patients with RA and juvenile idiopathic arthritis (JIA) in our hospitals in the last decade. METHODS: The study included 15 women, with 20 pregnancies, 19 childbirths, and one fetal death recorded between 2009 and 2018. We analyzed patient characteristics, disease activity, the modified total Sharp score (mTSS), and ΔmTSS from prepregnancy to delivery and from delivery to one year after delivery in the biologics (BIO) group (biologics used before pregnancy) and non-BIO group (not using biologics). RESULTS: There were five preterm births and seven low-birth-weight infants. The Clinical Disease Activity Index (CDAI) before pregnancy and postdelivery worsened from 12±1.8 to 19.9±2.7 (p<0.05). The mTSS at prepregnancy and postdelivery was 47.7±12.2 and 57.3±11.1 in the BIO group, respectively, and 58.9±11.9 and 75.0±13.1 in the non-BIO group, respectively. In addition, the ΔmTSS value from prepregnancy to delivery and from delivery to one year after delivery was 14.5±4.8 and 9.2±1.7 in the BIO group, respectively (p<0.05), and 16.1±5.2 and 8.3±4.0 in the non-BIO group, respectively. CONCLUSION: The disease activity worsened, and bone and joint destruction progressed in both the BIO and non-BIO groups during the perinatal period in adult patients with RA and JIA in the last decade.

Unsuccessful Intervention of CT-Assisted Osteosynthesis for Stress Fractures of the Hook of the Hamate: A Report of 3 Cases.

CASE: We performed computed tomography (CT)-assisted dorsal approach osteosynthesis for stress fractures of the hook of the hamate using the dorsal approach in 3 high school baseball players in the hybrid operating room. Bony union was observed in all patients on CT. All patients were able to play baseball without pain for at least 6 months after surgery. However, refractures were observed in all patients at a mean 9.7 months after surgery. CONCLUSION: The indications of osteosynthesis for stress fractures of the hook of the hamate in baseball players should be carefully considered.

Forefoot Deformities in Patients with Rheumatoid Arthritis: Mid- to Long-Term Result of Joint-Preserving Surgery in Comparison with Resection Arthroplasty.

BACKGROUND: Joint-preserving surgery for the forefoot has been increasingly performed for rheumatoid arthritis (RA). We compared joint-preserving surgeries with resection arthroplasty for RA in the forefoot. METHODS: Forefoot surgeries were performed on 62 toes in 42 patients with RA (men: 2; women: 40) between 2002 and 2018. Three groups were compared: PP-31 toes treated with joint-preserving surgery involving the modified Mann method for the big toe and offset osteotomy for lesser toes, PR-15 toes treated with joint-preserving surgery for the big toe and resection arthroplasty for lesser toes, and RR-16 toes treated with resection arthroplasty for all the toes. RESULTS: The PP group had significantly higher mean scores on a scale for RA in the foot and ankle at the latest follow-up than the RR group (86 vs. 75 points; p < 0.05). Hallux valgus (angle > 20°) of the big toe at the latest follow-up recurred in 10 (32%), 9 (60%), and 16 (100%) patients in the PP, PR, and RR groups, respectively. A revision surgery was performed in one patient each in the PP and PR groups. CONCLUSIONS: Joint-preserving surgery is superior to resection arthroplasty in preventing function loss and the recurrence of hallux valgus.

Strategy for the treatment of lateral epicondylitis of the elbow using denervation surgery.

BACKGROUND: A number of treatments for lateral epicondylitis of the elbow have been described. We have developed a strategy for the treatment of this condition. METHODS: We diagnosed lateral epicondylitis of the elbow in 86 patients. Conservative treatment resulted in resolution in 71 patients. Surgery was required in the remaining 15 patients. If the posterior branch of the posterior cutaneous nerve of the forearm showed a positive response to local anesthesia (block test), we performed denervation surgery on the posterior branch of the posterior cutaneous nerve of the forearm. Patients were asked to rate the degree of pain and sensory disturbance using a visual analog scale; the 11-item version of the Disabilities of the Arm, Shoulder and Hand measure; and the Patient-Rated Elbow Evaluation. RESULTS: A positive response to the block test was seen in 10 elbows (67%). After denervation surgery, pain relief was seen in 9 of 10 elbows (90%). The mean follow-up period was 30.4 months. At final follow-up, the average scores on the visual analog scale, 11-item version of the Disabilities of the Arm, Shoulder and Hand, and Patient-Rated Elbow Evaluation were 4.3 mm, 10.45 points, and 5.9 points, respectively. In the early period after denervation surgery, sensory disturbance was observed in 9 cases (90%). CONCLUSION: Our strategy of denervation surgery for lateral epicondylitis of the elbow was effective for pain relief among patients showing a positive response to the block test.

Immunohistochemical Analysis of Inflammatory Rheumatoid Synovial Tissues Using Anti-Human Podoplanin Monoclonal Antibody Panel.

Podoplanin (PDPN) is a transmembrane sialoglycoprotein, which is expressed in several normal tissues and malignant tumors. Although PDPN expression in rheumatoid arthritis (RA) has been reported, the role of PDPN in RA and other arthritic conditions has not been fully elucidated. In this study, we examined PDPN expression in inflammatory synovial tissues using an anti-human PDPN (hPDPN) monoclonal antibody (mAb) panel to select the most useful one for evaluation of synovitis. Synovial tissue samples were obtained from 11 RA patients and 9 osteoarthritis (OA) patients undergoing joint surgery. PDPN-positive cells were immunostained by a panel of PDPN mAbs (NZ-1, LpMab-3, LpMab-7, LpMab-10, LpMab-12, LpMab-13, and LpMab-17), followed by cell grading of inflammation and cell counting of PDPN-positivity by a quantitative analyzer. Immunohistochemistry showed that PDPN was markedly expressed in both macrophage-like type A and fibroblast-like type B lining cells of the hyperplastic synovial lining cell layer, and macrophages and fibroblasts in the stroma of RA. Among anti-PDPN mAbs, LpMab-12 showed the highest score. In inflammatory OA synovium, PDPN expression was also detectable. Although LpMab-12 also showed the highest score in OA, the difference was not statistically significant. The inflammatory synovitis score of RA was significantly higher than that of OA. PDPN was expressed in inflammatory lining cells and sublining stroma of RA and OA synovium. In the seven anti-hPDPN antibodies examined, LpMab-12 was the most stainable antibody for PDPN in RA synovitis. Thus, LpMab-12 for PDPN has a possible and promising specific biomarker for evaluating synovitis in RA and inflammatory OA.

Comparison of the Effects of Osteochondral Autograft Transplantation With Platelet-Rich Plasma or Platelet-Rich Fibrin on Osteochondral Defects in a Rabbit Model.

BACKGROUND: Although osteochondral autograft transplantation (OAT) provides satisfactory outcomes for osteochondral defects, for large defects OAT is often inadequate because of graft availability. Osteochondral allograft transplantation is an alternative treatment for large defects, but this approach is limited by graft storage constraints and carries disease transmission risks. Platelet-rich fibrin (PRF) is a second-generation platelet concentrate, and its positive effect on articular cartilage has been reported. However, the effect of PRF with OAT of osteochondral defects is unknown. PURPOSE: To compare the effects of OAT with platelet-rich plasma (PRP) and PRF on osteochondral defects in a rabbit model. STUDY DESIGN: Controlled laboratory study. METHODS: Forty-two juvenile rabbits were divided into control, PRP, and PRF groups. In the control and PRP groups, a cylindrical osteochondral defect (5 mm in diameter and 2 mm in depth) was created on the patellar groove, and an osteochondral graft (3.5 mm in diameter and 5 mm in length) harvested from the contralateral side was inserted into the distal portion of the defect. After wound closure, either normal saline or PRP was injected in the knee. In the PRF group, a PRF clot was placed in the defect before grafting. The surgical site was macroscopically and histologically assessed after 3 and 12 weeks. RESULTS: At 3 weeks, the PRF group (n = 8) was macroscopically healed compared with the other 2 groups (control, n = 7; PRP, n = 6) ( P < .005). Histologically, osteochondral graft cartilage of the PRF group had normal cellularity and higher amounts of safranin O staining relative to the other 2 groups ( P < .005). At 12 weeks, all 3 groups (n = 8 per group) were macroscopically healed with normal or nearly normal cartilage, and osteochondral graft cartilage was histologically hyaline cartilage. In contrast, the PRF group healed with hyaline-like cartilage at nongrafted defects, whereas the other 2 groups healed with fibrocartilage ( P < .001). CONCLUSION: OAT with PRF maintained hyaline cartilage, and the nongrafted defect healed with hyaline-like cartilage. CLINICAL RELEVANCE: PRF has the potential to improve clinical outcomes of OAT used to treat osteochondral lesions.

Characterization of the Anti-Bovine Podoplanin Monoclonal Antibody PMab-44.

A type I transmembrane sialoglycoprotein podoplanin (PDPN) is expressed in several normal cells, including podocytes of the kidney, type I alveolar cells of the lung, and lymphatic endothelial cells. We recently produced an anti-bovine PDPN (bovPDPN) monoclonal antibody (mAb), PMab-44, by immunizing mice with recombinant proteins of bovPDPN. In this study, we determined the critical epitope of PMab-44 for the recognition of bovPDPN using many deletion mutants and point mutants of bovPDPN. Flow cytometric analyses revealed that the epitope of PMab-44 was Glu46-Thr50, which corresponds to platelet aggregation-stimulating (PLAG) domain-3. The important amino acids in the PMab-44 epitope were determined to be Glu46, Tyr48, and Thr50. Western blot analysis also confirmed these results, indicating that the PLAG domain of bovPDPN is also important in immunogenicity for producing useful anti-PDPN mAbs.

Development and characterization of anti-glycopeptide monoclonal antibodies against human podoplanin, using glycan-deficient cell lines generated by CRISPR/Cas9 and TALEN.

Human podoplanin (hPDPN), which binds to C-type lectin-like receptor-2 (CLEC-2), is involved in platelet aggregation and cancer metastasis. The expression of hPDPN in cancer cells or cancer-associated fibroblasts indicates poor prognosis. Human lymphatic endothelial cells, lung-type I alveolar cells, and renal glomerular epithelial cells express hPDPN. Although numerous monoclonal antibodies (mAbs) against hPDPN are available, they recognize peptide epitopes of hPDPN. Here, we generated a novel anti-hPDPN mAb, LpMab-21. To characterize the hPDPN epitope recognized by the LpMab-21, we established glycan-deficient CHO-S and HEK-293T cell lines, using the CRISPR/Cas9 or TALEN. Flow cytometric analysis revealed that the minimum hPDPN epitope, in which sialic acid is linked to Thr76, recognized by LpMab-21 is Thr76-Arg79. LpMab-21 detected hPDPN expression in glioblastoma, oral squamous carcinoma, and seminoma cells as well as in normal lymphatic endothelial cells. However, LpMab-21 did not react with renal glomerular epithelial cells or lung type I alveolar cells, indicating that sialylation of hPDPN Thr76 is cell-type-specific. LpMab-21 combined with other anti-hPDPN antibodies that recognize different epitopes may therefore be useful for determining the physiological function of sialylated hPDPN.

Development of RAP Tag, a Novel Tagging System for Protein Detection and Purification.

Affinity tag systems, possessing high affinity and specificity, are useful for protein detection and purification. The most suitable tag for a particular purpose should be selected from many available affinity tag systems. In this study, we developed a novel affinity tag called the "RAP tag" system, which comprises a mouse antirat podoplanin monoclonal antibody (clone PMab-2) and the RAP tag (DMVNPGLEDRIE). This system is useful not only for protein detection in Western blotting, flow cytometry, and sandwich enzyme-linked immunosorbent assay, but also for protein purification.

PcMab-47: Novel Antihuman Podocalyxin Monoclonal Antibody for Immunohistochemistry.

Podocalyxin (PODXL) is a CD34-related sialomucin and a well-known marker of embryonic stem cells. PODXL is expressed in many types of tumors including colorectal cancers, breast cancers, and brain tumors. Overexpression of PODXL is an independent predictor of progression, metastasis, and poor outcome. PODXL is also expressed in many normal cells such as renal podocytes and endothelial cells (ECs). However, high-sensitive and high-specific anti-PODXL monoclonal antibodies (mAbs) have not been established. Herein, we immunized mice with recombinant human PODXL, which was produced using LN229 glioblastoma cells. The anti-PODXL mAb, PcMab-47, reacted with endogenous PODXL-expressing cancer cell lines and normal cells independently of glycosylation in flow cytometry. Immunohistochemical analysis showed that PcMab-47 detected PODXL-expressing normal cells such as podocytes of kidney or ECs. Furthermore, PcMab-47 stained PODXL-expressing cancer cells of colon or breast cancers. These results suggest that PcMab-47 could be useful for investigating the expression and function of PODXL in cancers and normal tissues.

Antiglycopeptide Mouse Monoclonal Antibody LpMab-21 Exerts Antitumor Activity Against Human Podoplanin Through Antibody-Dependent Cellular Cytotoxicity and Complement-Dependent Cytotoxicity.

The interaction between podoplanin (PDPN) and C-type lectin-like receptor 2 (CLEC-2) is involved in tumor malignancy. We have established many monoclonal antibodies (mAbs) against human podoplanin using the cancer-specific mAb (CasMab) technology. LpMab-21, one of the mouse antipodoplanin mAbs, is of the IgG2a subclass, and its minimum epitope was determined to be Thr76-Arg79 of the human podoplanin. Importantly, sialic acid is linked to Thr76; therefore, LpMab-21 is an antiglycopeptide mAb (GpMab). In this study, we investigated whether LpMab-21 shows antibody-dependent cellular cytotoxicity (ADCC) and complement-dependent cytotoxicity (CDC) against human podoplanin-expressing cancer cell lines in vitro and also studied its antitumor activities using a xenograft model. LpMab-21 showed high ADCC and CDC activities against not only podoplanin-expressing Chinese hamster ovary cells but also LN319 glioblastoma cells and PC-10 lung cancer cells, both of which endogenously express podoplanin. Furthermore, LpMab-21 decreased tumor growth in vivo, indicating that LpMab-21 could be useful for antibody therapy against human podoplanin-expressing cancers.

DaMab-2: Anti-Human DGKα Monoclonal Antibody for Immunocytochemistry.

Diacylglycerol kinase (DGK) is responsible for the enzymatic conversion of diacylglycerol to phosphatidic acid. Since both diacylglycerol and phosphatidic acid serve as signaling molecules, DGK is regarded as a hub between diacylglycerol-mediated and phosphatidic acid-mediated signaling. One of the 10 DGK isozymes, DGKα, is shown to be involved in T cell function. Transfection studies using tagged expression vectors revealed that DGKα localizes to the cytoplasm and nucleus and translocates to the plasma membrane in response to T cell receptor stimulation. However, a limited number of studies reported the localization of native protein of DGKα in tissues and cells. In this study, we immunized mice with recombinant DGKα and developed several anti-DGKα monoclonal antibodies (mAbs). One of the established anti-DGKα mAbs is a clone DaMab-2 (mouse IgG1, kappa). In enzyme-linked immunosorbent assay, DaMab-2 recognized only DGKα, and did not react with the other isozymes, such as DGKγ, DGKζ, DGKη, and DGKδ. Importantly, DaMab-2 is very useful in immunocytochemical analysis of human cultured cells, indicating that DaMab-2 is advantageous to analyze the localization and function of DGKα.

Specific Detection of Dog Podoplanin Expressed in Renal Glomerulus by a Novel Monoclonal Antibody PMab-38 in Immunohistochemistry.

Podoplanin (PDPN) is expressed in several normal tissues including podocytes of renal glomerulus, lymphatic endothelial cells (LECs), and type I alveolar cells of lung. PDPN activates platelet aggregation by binding to C-type lectin-like receptor-2 (CLEC-2) on platelets. Many monoclonal antibodies (mAbs) against human PDPN, mouse PDPN, rat PDPN, rabbit PDPN, and bovine PDPN have been established; antidog PDPN (dPDPN) mAbs have not been developed. Herein, we immunized mice with the recombinant proteins of dPDPN and developed anti-dPDPN mAbs. One of the clones, PMab-38, is useful for detecting podocytes in immunohistochemical analysis; in contrast, it did not react with LECs or type I alveolar cells. PMab-38 also detected dPDPN specifically in flow cytometry and Western blot analysis. PMab-38 is expected to be useful for investigating the function of dPDPN, which is expressed in podocytes.

LpMab-12 Established by CasMab Technology Specifically Detects Sialylated O-Glycan on Thr52 of Platelet Aggregation-Stimulating Domain of Human Podoplanin.

Podoplanin (PDPN), also known as Aggrus, possesses three tandem repeat of platelet aggregation-stimulating (PLAG) domains in its N-terminus. Among the PLAG domains, sialylated O-glycan on Thr52 of PLAG3 is essential for the binding to C-type lectin-like receptor-2 (CLEC-2) and the platelet-aggregating activity of human PDPN (hPDPN). Although various anti-hPDPN monoclonal antibodies (mAbs) have been generated, no specific mAb has been reported to target the epitope containing glycosylated Thr52. We recently established CasMab technology to develop mAbs against glycosylated membrane proteins. Herein, we report the development of a novel anti-glycopeptide mAb (GpMab), LpMab-12. LpMab-12 detected endogenous hPDPN by flow cytometry. Immunohistochemical analyses also showed that hPDPN-expressing lymphatic endothelial and cancer cells were clearly labeled by LpMab-12. The minimal epitope of LpMab-12 was identified as Asp49-Pro53 of hPDPN. Furthermore, LpMab-12 reacted with the synthetic glycopeptide of hPDPN, corresponding to 38-54 amino acids (hpp3854: 38-EGGVAMPGAEDDVVTPG-54), which carries α2-6 sialylated N-acetyl-D-galactosamine (GalNAc) on Thr52. LpMab-12 did not recognize non-sialylated GalNAc-attached glycopeptide, indicating that sialylated GalNAc on Thr52 is necessary for the binding of LpMab-12 to hPDPN. Thus, LpMab-12 could serve as a new diagnostic tool for determining whether hPDPN possesses the sialylation on Thr52, a site-specific post-translational modification critical for the hPDPN association with CLEC-2.