Patient-centred screening for primary immunodeficiency: a multi-stage diagnostic protocol designed for non-immunologists

New frontiers of primary antibody deficiencies

Primary antibody deficiencies (PAD) form the largest group of inherited disorders of the immune system. They are characterized by a marked reduction or absence of serum immunoglobulins (Ig) due to disturbed B cell differentiation and by a poor response to vaccination. PAD can be divided into agammaglobulinemia, Ig class switch recombination deficiencies, and idiopathic hypogammaglobulinemia. Over the past 20 years, defects have been identified in 18 different genes, but in many PAD patients the underlying gene defects have not been found. Diagnosis of known PAD and discovery of new PAD is important for good patient care. In this review, we present the effects of genetic defects in the context of normal B cell differentiation, and we discuss how new technical developments can support understanding and discovering new genetic defects in PAD.

Severe combined immunodeficiency in Greek children over a 20-year period: rarity of γc-chain deficiency (X-linked) type

Severe combined immunodeficiencies (SCID) are a heterogeneous group of genetic disorders characterized by a blockade or impairment of both cellular and humoral immunity. Several epidemiological studies in different geographic areas have shown that the most common type of SCID affecting almost half of these patients is the X-linked common γ-chain (γ(c)) deficiency. The objective of the study was to document the incidence and types of SCID in our area. We conducted a retrospective analysis of patients who were diagnosed with SCID in the major immunology center in Greece for a 20-year period. During the study period, 30 children from 27 unrelated families with final diagnosis of SCID were identified. The incidence of SCID in Greece is estimated at 1.7 cases per 100,000 live births. Out of 30 children, 19 were boys (63.3%) and 26 (86.7%) had Greek maternal origin. Lymphocyte immunophenotypes that were identified were T(-)B(-)NK(+) in 12 (40%) children, T(-)B(+)NK(-) in six (20%), T(-)B(+)NK(+) in three (10%), T(-)B(-)NK(-) in two (6.7%) and T(+)B(+/-)NK(+) in seven (23.4%) (among them, four [13.4%] females with Omenn's syndrome). Molecular diagnosis was available for 12 children: γ(c) (2) with non Greek maternal origin, Jak3 (2), Rag1 (2), Artemis (3), ADA deficiency (2), PNP deficiency (1). Out of the 26 children of Greek maternal origin diagnosed with SCID representing 23 distinct families, only two (8.7%) had lymphocyte immunophenotype compatible with γ(c)-chain gene mutation (no molecular testing or enough DNA was available for them at the time of diagnosis). Findings of the present study suggest that, for unknown reasons, mutations of the γ(c) chain of several cytokine receptors have a rare occurrence in our area.

Critical issues and needs in management of primary immunodeficiency diseases in Latin America

Experts from six Latin American countries met to discuss critical issues and needs in the diagnosis and management of primary immunodeficiency diseases (PIDD). The diagnosis of PIDD is generally made following referral to an immunology centre located in a major city, but many paediatricians and general practitioners are not sufficiently trained to suspect PIDD in the first place. Access to laboratory testing is generally limited, and only some screening tests are typically covered by government health programmes. Specialised diagnostic tests are generally not reimbursed. Access to treatment varies by country reflecting differences in healthcare systems and reimbursement policies. An online PIDD Registry Programme for Latin America has been available since 2009, which will provide information about PIDD epidemiology in the region. Additional collaboration across countries appears feasible in at least two areas: a laboratory network to facilitate the diagnosis of PIDD, and educational programmes to improve PIDD awareness. In total, these collaborations should make it possible to advance the diagnosis and management of PIDD in Latin America.

Educational paper. The expanding clinical and immunological spectrum of severe combined immunodeficiency

Severe combined immunodeficiency (SCID) is one of the most severe forms of primary immunodeficiency characterized by absence of functional T lymphocytes. It is a paediatric emergency, which is life-threatening when recognized too late. The clinical presentation varies from the classical form of SCID through atypical SCID to Omenn syndrome. In addition, there is a considerable immunological variation, which can hamper the diagnosis. In this educational review, we describe the immunopathological background, clinical presentations and diagnostic process of SCID, as well as the therapeutic possibilities.

Educational paper: Primary immunodeficiencies in children: a diagnostic challenge

Primary immunodeficiencies (PIDs) are characterized by an increased susceptibility to infections due to defects in one ore more components of the immune system. Although most PIDs are relatively rare, they are more frequent than generally acknowledged. Early diagnosis and treatment of PIDs save lives, prevent morbidity, and improve quality of life. This early diagnosis is the task of the pediatrician who encounters the child for the first time: he/she should suspect potential PID in time and perform the appropriate diagnostic tests. In this educational paper, the first in a series of five, we will describe the most common clinical presentations of PIDs and offer guidelines for the diagnostic process, as well as a brief overview of therapeutic possibilities and prognosis.

[Consensus Document on the differential diagnosis and therapeutic approach to recurrent fever by the Paediatric Infectology Society and the Paediatric Rheumatology Society]

Recurrent fever is a relatively common problem during childhood. Diagnosis is often easy and related to mild viral infections. However a small proportion of these cases originate from an underlying non-infectious process that is generally difficult to diagnose. In this paper we describe the differential diagnosis of recurrent or periodic fever versus other processes, with especial attention to autoinflammatory disorders (AD). AD are alterations of innate immunity, and they have been recently classified as an immunodeficiency. Anyhow, since infections are not present, these processes are different to the classic primary immunodeficiency. An important part of AD is of known genetic aetiology. The symptoms originate from an underlying inflammatory process and can have different clinical expressions. One of the most relevant groups is the hereditary syndromes of periodic fever. This group of diseases associates recurrent fever and several clinical symptoms with a relative periodicity, separated by intervals free or almost free of symptoms. We include the diagnostic criteria for some processes as well as the characteristics that should, eventually, lead to a genetic study. Although treatment should be individualised, we also include some general recommendations.

Severe axillary lymphadenitis after BCG vaccination: alert for primary immunodeficiencies

The bacilli Calmette-Guérin (BCG) vaccine is administered to all newborns in countries where tuberculosis is endemic. Immunocompromised hosts, namely patients with human immunodeficiency virus infection or primary immunodeficiencies, are especially prone to serious complications from this vaccine. We report three cases of BCG disease in children with primary immunodeficiencies: one with a partial recessive interferon-γ receptor 1 deficiency, who developed BCG dissemination; and two relatives with ZAP70 deficiency, a severe combined immunodeficiency, both of whom presented with regional and distant BCG disease. All had severe axillary lymphadenitis. These clinical cases underline the importance of considering the diagnosis of immunodeficiency in a child with severe axillary lymphadenitis after BCG vaccination and of disseminated BCG disease in an immunodeficient child in the appropriate clinical setting. Moreover, BCG vaccination should be delayed in every newborn with a family history of primary immunodeficiency until the condition has been ruled out.

Immune function in hypopituitarism: time to reconsider?

Hypopituitarism is not currently considered as a potential cause of immune disruption in humans. Accumulating data from in vitro and animal models support a role for the pituitary gland in immune regulation. Furthermore, the increased mortality risk noted in patients with adult hypopituitarism remains poorly explained and immune dysfunction could conceivably contribute to this observation. In a recent issue of Clinical & Experimental Immunology, we presented new data relating to immune status in adults with treated, severe hypopituitarism. We observed humoral immune deficiency in a significant proportion, despite stable pituitary replacement, including growth hormone (GH). This was especially evident in those with low pretreatment IGF-I levels and appeared independent of anticonvulsant use or corticosteroid replacement. These observations require substantiation with future studies. In this short review, we summarize existing data relating to the effects of pituitary hormones on immune function and discuss potential clinical implications surrounding the hypothesis of immune dysregulation in severe hypopituitarism.

Technical and diagnostic performance of five commercial anti-diphtheria toxoid IgG enzyme-linked immunosorbent assay kits

The technical and diagnostic performances of five commercially available enzyme-linked immunosorbent assays for the measurement of anti-diphtheria toxoid IgG antibodies were evaluated. There was good agreement between the relative sensitivities of the five assays, but the relative specificity of one of the assays differed from that of the other four assays. Three of the five assays possessed recoveries of the international reference material NIBSC 00/496 within the range of 90% to 110% at antibody levels >0.1 IU/ml. The data suggest that there are manufacture-dependent differences in relative sensitivity, specificity, and accuracy for the determination of anti-diphtheria toxoid IgG antibodies that could result in different diagnostic interpretations.

Bioinformatics services related to diagnosis of primary immunodeficiencies

PURPOSE OF REVIEW

Most primary immunodeficiencies (PIDs) have overlapping signs and symptoms - presenting a challenge for diagnosis. The information available from the Internet for over 200 PIDs is scattered between numerous services and databases. Patient information has been collected in different patient registries. Several software tools have been developed in order to build the databases, expert systems and other information systems useful in diagnosis or prediction.

RECENT FINDINGS

Previously released services have been significantly improved and some new bioinformatics tools have been developed to help in diagnosis, prediction, mutation analysis and classification of PIDs. Several national initiatives have been launched for centralized PID information services. The very latest additions are tools and approaches for PID candidate gene prioritization, systematic classification and a medical expert system to help in diagnosis.

SUMMARY

Many bioinformatics tools for PIDs are already freely available over the Internet. We expect bioinformatics tools to further help healthcare professionals in diagnosis, analysis and prediction. Currently, most of the resources are stand-alone and thus their integration will be a challenge for the future. Another challenge is to develop terminologies, ontologies and standards to achieve semantic interoperability.

Children with frequent infections: a proposal for a stepwise assessment and investigation of the immune system

Although many children develop frequent infections, only a few have an underlying immune disorder. Children with dysfunction of the immune system develop frequent infections and/or recurrent, persistent, severe, and rare infections. The aim of this review is to provide to the clinician a valuable tool for recognizing any 'discords' of the 'immune-system symphonic orchestra'. By following a reverse route, it will be possible to brighten up the dark and winding road of immunodeficiencies and identify the exact point of immune dysfunction. This is fundamental and crucial to perceive etiologic management and subsequently achieve the best for these young patients and their families.

Primary antibody deficiencies: recognition, clinical diagnosis and referral of patients

The primary antibody deficiency syndromes are a rare group of immunodeficiencies where diagnostic delay remains common due to limited awareness of the existence and heterogeneity of their presenting features. Referral for specialist assessment leads to earlier diagnosis and appropriate therapy to prevent or limit structural organ and tissue damage. Greater education of healthcare professionals is required to ensure prompt recognition and referral to specialists with expertise in the care of primary immunodeficiencies, especially since study of these rare conditions is a minor part of undergraduate and general postgraduate training. Greater awareness would lead to reduced morbidity, improved quality of life and survival outcomes in this patient group.

The outcome of patients with unclassified hypogammaglobulinemia in early childhood

Symptomatic hypogammaglobulinemia in childhood may be the initial finding of primary immunodeficiency (PID) or may be due to delay in maturation of immunoglobulin synthesis. The aim of this study was to review the clinical and laboratory records of patients with unclassified hypogammaglobulinemia and to evaluate whether these children experience changes in serum immunoglobulin concentrations during long-term followup and have an exact diagnosis in natural course of disease. We reviewed the data of 412 patients who were diagnosed as PID with symptomatic hypogammaglobulinemia. Thirty-seven patients with hypogammaglobulinemia [19 males (51.4%) and 18 females (48.6%), with a followup of 34.1 +/- 22.0 months] who were not classified according to European Society for Immunodeficiencies diagnostic criteria were included in this study. The mean age at the beginning of the symptoms was 21.4 +/- 20.6 months and the mean age at admission was 51.5 +/- 25.8 months. The commonest clinical presentations were recurrent upper (94.6%) and/or lower (40.5%) respiratory infections, urinary infection (27%) and gastroenteritis (10.8%). Percentage of consanguinity was 8%. Of the initial 37 patients, 18 (48.6%) spontaneously corrected their immunoglobulin abnormalities during followup. Clinical symptoms of these patients were also improved. IgG, IgA and IgM levels reached to normal levels at ages 62.5 +/- 21.8, 72.0 +/- 11.2, 55.2 +/- 7.8 months, respectively. In remaining 19 patients with undefined/unclassified hypogammaglobulinemia, three partial IgA deficiency, seven IgG subclass deficiency, two selective IgM deficiency and two common variable immunodeficiency (CVID) were diagnosed by long-term monitoring of immunoglobulin levels. Five (13.5%) of the 37 unclassified patients could not be exactly diagnosed while two of them might have a T-cell defect and three of them still had low IgG and IgA levels but adequate antibody responses against vaccine antigens. In conclusion, it is important to monitor symptomatic patients with hypogammaglobulinemia periodically. Some children may spontaneously correct their immunoglobulin abnormalities not in the first 30 months of age, but during the first decade of life and some of them may have a severe PID like CVID.

A decreased frequency of regulatory T cells in patients with common variable immunodeficiency

Introduction

Common variable immunodeficiency disorder (CVID) is a heterogeneous syndrome, characterized by deficient antibody production and recurrent bacterial infections in addition abnormalities in T cells. CD4⁺CD25^high regulatory T cells (Treg) are essential modulators of immune responses, including down-modulation of immune response to pathogens, allergens, cancer cells and self-antigens.

Objective

In this study we set out to investigate the frequency of Treg cells in CVID patients and correlate with their immune activation status.

Materials and Methods

Sixteen patients (6 males and 10 females) with CVID who had been treated with regular intravenous immunoglobulin and 14 controls were enrolled. Quantitative analyses of peripheral blood mononuclear cells (PBMC) were performed by multiparametric flow cytometry using the following cell markers: CD38, HLA-DR, CCR5 (immune activation); CD4, CD25, FOXP3, CD127, and OX40 (Treg cells); Ki-67 and IFN-γ (intracellular cytokine).

Results

A significantly lower proportion of CD4⁺CD25^highFOXP3 T cells was observed in CVID patients compared with healthy controls (P<0.05). In addition to a higher proportion of CD8⁺ T cells from CVID patients expressing the activation markers, CD38⁺ and HLA-DR⁺ (P<0.05), we observed no significant correlation between Tregs and immune activation.

Conclusion

Our results demonstrate that a reduction in Treg cells could have impaired immune function in CVID patients.

Intrinsic defect of the immune system in children with Down syndrome: a review

Down syndrome (DS) is the most frequent cause of mental retardation in man. Immunological changes in DS have been observed since the 1970s. The neurological system appears to be ageing precociously, with early occurrence of Alzheimer disease; until now, the observed immunological differences have been interpreted in the same context. Looking back at past and present results of immunological studies in DS children in relation to the clinical consequences they suffer, we conclude that it is more likely that the DS immune system is intrinsically deficient from the very beginning.

Common variable immunodeficiency: 20-yr experience at a single centre

Common variable immunodeficiency (CVID) is the most common symptomatic primary immunodeficiency. It can present at any age in patients with a history of recurrent bacterial infections, with or without a family history of other primary immunodeficiencies (PID), and shows a wide range of clinical manifestations and immunological data. Diagnosis is based on low IgG, IgM and/or IgA levels. Delayed diagnosis and therapy can lead to bronchiectasis and malabsorption. The aim of this study was to describe a paediatric population diagnosed of CVID and its evolution in the population. Memory B-cell (MB) classification carried out in these patients was correlated with clinical manifestations and outcome. Clinical and immunological data of 22 CVID children under 18 yr treated at our centre between 1985 and 2005 are presented. Immunological studies included those for diagnosis and MB quantification. Differences in form of presentation, familial incidence and MB classification were reviewed. A statistical descriptive analysis was made. Infections were the commonest manifestation, affecting mainly respiratory (19/22) and gastrointestinal (10/22) tracts. Bronchiectasis was present in seven cases, and detected prior to CVID diagnosis in five. Replacement therapy led to a significant reduction in the number of infections. Severe complications appeared mostly in patients without MB. Patients of the same family share the same MB group. Family members had also been diagnosed of CVID in seven cases. Early diagnosis and therapy are essential to improve outcome in these patients. MB studies are useful in children to orient prognosis and further genetic studies.

Antibody deficiency: Table 1

Antibody deficiencies may arise as primary disorders or secondary to a variety of diseases, drugs and other environmental/iatrogenic factors. Significant primary antibody deficiencies are relatively rare but, collectively, account for the majority of primary immunodeficiency syndromes encountered in clinical practice. The genetic basis of a number of primary deficiencies has been clarified, although there is considerable genotype/phenotype heterogeneity and the role of gene/environment interactions has yet to be fully elucidated. Primary antibody deficiency can present at any age. The hallmark clinical presentation is recurrent bacterial infection, but these disorders are also associated with a wide variety of other infectious and non-infectious complications and with a high incidence of chronic, structural tissue damage, particularly in the respiratory tract. Clinical recognition of primary antibody deficiency is frequently delayed with consequent increased morbidity, diminished quality of life and early mortality. Clinical laboratories can contribute to improved and timely detection through awareness of routine test results which may be overtly or indirectly suggestive of antibody deficiency. Secondary deficiency is associated with increased awareness, better recognition and earlier diagnosis than in primary disorders. Early liaison and referral of patients with suspected antibody deficiency for specialist opinion and prompt, appropriate therapy is central to the achievement of good clinical outcomes.

Approach to the patient with recurrent infections

Children with a history of recurrent or unusual infections present a diagnostic challenge. Differentiation between frequent infections caused by common risk factors, versus primary immune dysfunction should be based on a detailed history and physical examination and, if indicated, followed by appropriate laboratory studies. A high index of suspicion could lead to an early diagnosis and treatment of an underlying immune deficiency disease. This article presents to physicians an approach to the evaluation of children with recurrent infections. Important details from the history and physical examination, and an appropriate choice of screening laboratory test to be ordered in a given situation are discussed.

Clinical immunology review series: an approach to the patient with recurrent superficial abscesses

Patients may be referred to the immunology clinic for investigation of recurrent superficial abscess formation. In the majority of adult patients this clinical presentation does not equate with an underlying primary immune deficiency. Nevertheless, recurrent mucocutaneous abscesses can be associated with significant morbidity and long-term complications, including scarring and fistula formation, and may be associated with underlying immune-mediated disease. This review sets out an approach to the patient with recurrent superficial abscesses, focusing on the differential diagnoses, investigation and management of both the common causes and those associated with specific immune deficiency.

Clinical immunology review series: an approach to the patient with recurrent infections in childhood

Recurrent or persistent infection is the major manifestation of primary immunodeficiency, which also results in atypical infection with opportunistic organisms. Young children are also vulnerable to infection and recurrent infection is common. While most children with recurrent infection have a normal immunity, it is important to recognize the child with an underlying primary immunodeficiency and investigate and treat appropriately and yet not over investigate normal children. Prompt, accurate diagnosis directs the most appropriate treatment, and early and judicious use of prophylactic antibiotics and replacement immunoglobulin can prevent significant end organ damage and improve long-term outlook and quality of life. This paper describes important presenting features of primary immunodeficiency and indicates when further investigation is warranted.

Recognition, clinical diagnosis and management of patients with primary antibody deficiencies: a systematic review

The primary purpose of this systematic review was to produce an evidence-based review of the literature as a means of informing current clinical practice in the recognition, diagnosis and management of patients with suspected primary antibody deficiency. Randomized controlled trials (RCTs) were identified from a search of MEDLINE, EMBASE, The Cochrane Library, DARE (CRD website) and CINAHL by combining the search strategies with The Cochrane Collaboration's validated RCT filter. In addition, other types of studies were identified in a separate search of MEDLINE and EMBASE. Patients at any age with recurrent infections, especially in the upper and lower respiratory tracts, should be investigated for possible antibody deficiency. Replacement therapy with immunoglobulin in primary antibody deficiencies increases life expectancy and reduces infection frequency and severity. Higher doses of immunoglobulin are associated with reduced infection frequency. Late diagnosis and delayed institution of immunoglobulin replacement therapy results in increased morbidity and mortality. A wide variety of organ-specific complications can occur in primary antibody deficiency syndromes, including respiratory, gastroenterological, hepatic, haematological, neurological, rheumatological and cutaneous. There is an increased risk of malignancy. Some of these complications appear to be related to diagnostic delay and inadequate therapy. High-quality controlled trial data on the therapy of these complications is generally lacking. The present study has identified a number of key areas for further research, but RCT data, while desirable, is not always obtained easily for rare conditions. Few data from registries or large case-series have been published in the past 5 years and a greater focus on international collaboration and pooling of data is needed.

The European internet-based patient and research database for primary immunodeficiencies: results 2004-06

Because primary immunodeficiencies (PID) are rare diseases, transnational studies are essential to maximize the scientific outcome and lead to improved diagnosis and therapy. Immunologists in Europe have united to determine the prevalence of PID in Europe and to establish and evaluate harmonized guidelines for the diagnosis and treatment of PID as well as to improve the awareness of PID in Europe. In order to achieve this aim we have developed an internet-based database for clinical and research data on patients with PID. This database forms the platform for studies of demographics, the development of new diagnostic and therapeutic strategies and the identification of novel disease-associated genes. The database is completely secure, while providing access to researchers via a standard browser using password and encrypted log-in sessions and conforms to all European and national ethics and data protection guidelines. So far 2386 patients have been documented by 35 documenting centres in 20 countries. Common variable immunodeficiency (CVID) is the most common entity, accounting for almost 30% of all entries. First statistical analyses on the quality of life of patients show the advantages of immunoglobulin replacement therapy, at the same time revealing a mean diagnostic delay of over 4 years. First studies on specific questions on selected PID are now under way. The platform of this database can be used for any type of medical condition.

IDR knowledge base for primary immunodeficiencies

Background

The ImmunoDeficiency Resource (IDR) is a knowledge base for the integration of the clinical, biochemical, genetic, genomic, proteomic, structural, and computational data of primary immunodeficiencies. The need for the IDR arises from the lack of structured and systematic information about primary immunodeficiencies on the Internet, and from the lack of a common platform which enables doctors, researchers, students, nurses and patients to find out validated information about these diseases.

Description

The IDR knowledge base, first released in 1999, has grown substantially. It contains information for 158 diseases, both from a clinical as well as molecular point of view. The database and the user interface have been reformatted. This new IDR release has a richer and more complete breadth, depth and scope. The service provides the most complete and up-to-date dataset. The IDR has been integrated with several internal and external databases and services. The contents of the IDR are validated and selected for different types of users (doctors, nurses, researchers and students, as well as patients and their families). The search engine has been improved and allows either a detailed or a broad search from a simple user interface.

Conclusion

The IDR is the first knowledge base specifically designed to capture in a systematic and validated way both clinical and molecular information for primary immunodeficiencies. The service is freely available at http://bioinf.uta.fi/idr and is regularly updated. The IDR facilitates primary immunodeficiencies informatics and helps to parameterise in silico modelling of these diseases. The IDR is useful also as an advanced education tool for medical students, and physicians.

Early indicators of immunodeficiency in adults and children: protocols for screening for primary immunological defects

Early recognition of primary immunodeficiency is essential to reduce morbidity and mortality, and yet failure to recognize these conditions is still a major problem for clinicians around the world. The problem is that general practitioners, physicians and paediatricians lack familiarity with these rare disorders, and lack guidance regarding the appropriate use of immunological investigations. A working party from the European Society for Immunodeficiencies (ESID) has published screening protocols for these rare disorders, which aim to help select which tests should be done in which patients. The success of these proposals will depend on all immunologists disseminating this information in a format that is suitable for the busy generalist, who may not be familiar with these immunological tests and concepts. Laboratories should expect increasing requests for these screening investigations, and should make themselves familiar with these protocols so that appropriate second-line investigations can be arranged in a timely fashion. Speedy and effective communication between the laboratory and clinician is essential, and clinically interpreted reports are mandatory. Although these protocols are part of a screening process, their effectiveness in practice remains to be established, and further refinement will be required over time. The early involvement of the clinical immunologist in cases of suspected immunodeficiency is key.

Studies on trypsin inhibitor in barley. I. Purification and some properties

To clarify the properties and functions of a trypsin inhibitor from Japanese barley in comparison with the inhibitor from Pirkka barley, an inhibitor was isolated from the barley Hordeum distichum L var. emend Lamark by extraction with 1% NaCl, ammonium sulfate fractionation and repeated chromatography on DEAE-cellulose and CM-cellulose. The final purified preparation of the inhibitor was found to be homogeneous by both chromatographic and electrophoretic analysis. The inhibitor was thermostable and was stable over the broad pH range from 2 to 11. No inhibition was observed by heavy metal ions and many reagents at 10(-2) M, except that p-chloromercuribenzoate caused a 69% loss of activity. The inhibitor was subjected to isoelectric focusing at pH 7.51 and its molecular weight was calculated to be 14,200+/-900 by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate. The apparent dissociation constant for the complex between the inhibitor and trypsin[EC 3.4.21.4] was 1.64 X 10(-7)M with casein as a substrate. One microgram of purified inhibitor inhibited 1.5 mug of pure trypsin in the hydrolysis of alpha-N-benzoyl-DL-arginine-p-nitroanilide. By chemical modification of arginyl residues in the inhibitor with 1,2-cyclohexanedione, the inhibitor was shown to be an arginine inhibitor. The inhibitor contained relatively many basic amino acids and few half cystines as compared with Pirkka barley trypsin inhibitor.