Low IgG2 and polysaccharide response in a T cell receptor expression defect

B lymphocytes require appropriate T lymphocyte cooperation to synthesize immunoglobulins (Ig). Such interaction presumably takes place after engagement of the T cell receptor (TcR) by antigen. The present work addresses B lymphocyte function (and phenotype) in a novel type of immunodeficiency which is characterized by a TcR expression defect. In contrast to expectations, the two affected siblings that were studied displayed normal in vivo antibody responses to both endogenous and exogenous protein antigens. However, they showed impaired responses to certain polysaccharide antigens together with a selective IgG2 deficiency. These results suggest that some polysaccharide responses may be more T cell dependent than previously suspected, and support the notion that T cell dysfunctions (of this or other kind), rather than Ig gene deletions, may be the molecular basis of certain IgG2 deficiencies. To rule out a concomitant gross B cell dysfunction in these individuals, B lymphocyte phenotype and function were assayed in vitro, and found to be normal. A T cell line derived from one of the siblings displayed an abnormal TcR on the cell surface, but it showed several normal TcR-mediated functions. This suggests that the low number of peripheral T lymphocytes that have been found to express low TcR levels in these immunodeficiencies may be operational, and supplying sufficient "help" for the observed normal antibody responses to all tested protein, but not polysaccharide, antigens.     

Apparent genotype–phenotype correlation in childhood,adolescent, and adult Chediak‐Higashi syndrome

Chediak‐Higashi syndrome (CHS) is a rare autosomal recessive disorder characterized by severe immunologic defects, reduced pigmentation, bleeding tendency, and progressive neurological dysfunction. Most patients present in early childhood and die unless treated by bone marrow transplantation. About 10–15% of patients exhibit a much milder clinical phenotype and survive to adulthood, but develop progressive and often fatal neurological dysfunction. Very rare patients exhibit an intermediate adolescent CHS phenotype, presenting with severe infections in early childhood, but a milder course by adolescence, with no accelerated phase. Here, we describe the organization and genomic DNA sequence of the CHS1 gene and mutation analysis of 21 unrelated patients with the childhood, adolescent, and adult forms of CHS. In patients with severe childhood CHS, we found only functionally null mutant CHS1 alleles, whereas in patients with the adolescent and adult forms of CHS we also found missense mutant alleles that likely encode CHS1 polypeptides with partial function. Together, these results suggest an allelic genotype–phenotype relationship among the various clinical forms of CHS. © 2002 Wiley‐Liss, Inc.     

T lymphocyte anergy during acute infectious mononucleosis is restricted to the clonotypic receptor activation pathway.

The transient T cell anergy associated with acute infectious mononucleosis (IM) caused by the Epstein-Barr virus has been analysed in a sample of 14 IM children. Peripheral blood mononuclear cells (PBMC) obtained from IM patients showed a significant specific impairment in their proliferative response to both phytohaemagglutinin (PHA; P less than 0.05) and to an anti-CD3 MoAb (P less than 0.001), although both responses reached normal control levels by addition of a submitogenic dose of either phorbol myristate acetate (PMA) or recombinant IL-2 (rIL-2). In contrast, activation signals delivered through other surface molecules (CD2, CD28) or other transmembrane pathways (PMA plus a calcium ionophore) elicited normal or high proliferative responses in most IM PBMC. In a group of five patients tested, the synthesis of IL-2 by IM PBMC in the presence of PMA was impaired when PHA or anti-CD3 was used as stimulus, but it reached normal levels with anti-CD2 or ionophore. Lastly, PHA failed to induce IL-2 alpha receptor (IL-2R alpha) expression in IM PBMC from four tested patients, but the presence of PMA completely corrected this defect. Taken together, these results strongly suggest that the T cell anergy associated with acute IM is due to a T cell receptor (TCR)-specific impairment in the induction of genes involved in T cell proliferation (including those coding for IL-2 and IL-2R alpha) upon membrane signalling to otherwise normal T lymphocytes, since CD2, CD28 and certain transmembrane activation pathways are uncoupled from CD3 in these particular pathological conditions (and perhaps in most in vivo situations). This and other similar experimental approaches to transient secondary immunodeficiencies may help to unravel the physiopathological role of different surface molecules in T cell activation.     

Infliximab for treatment of pyoderma gangrenosum associated with inflammatory bowel disease

OBJECTIVES: Pyoderma gangrenosum is an immune-mediated inflammatory condition characterized by ulcerative skin lesions affecting 1-2% of patients with inflammatory bowel disease (IBD). Treatment includes wound care, antibiotics, corticosteroids, and immunomodulators. However, response to therapy varies, and many patients with pyoderma gangrenosum have disease that is refractory to these agents. The aim of this study was to assess the response of medically refractory pyoderma gangrenosum to infliximab. METHODS: This was a multicenter retrospective study of patients with IBD and medically refractory pyoderma gangrenosum treated with infliximab. Data collected included the following: baseline demographics; duration of IBD; history of bowel resection; duration of skin lesions; number, size, and location of pyoderma gangrenosum lesions; prior medications; dose and number of infliximab infusions; bowel activity before and after infliximab; pyoderma gangrenosum activity before and after infliximab therapy; time to response and time to healing of pyoderma gangrenosum lesions; recurrence of pyoderma gangrenosum after infliximab; corticosteroid taper; and adverse reactions to infliximab. RESULTS: There were 13 patients with moderate to severe pyoderma gangrenosum and IBD treated with infliximab. All patients demonstrated complete healing of the skin lesions. Three patients had a complete response to induction infliximab therapy and did not require additional treatment. Ten patients responded to induction infliximab and have maintained pyoderma gangrenosum healing with infusions every 4-12 wk. All patients receiving corticosteroids were able to discontinue them completely after institution of infliximab treatment. Infliximab was well tolerated; the only treatment-related adverse events were sunburn in one patient and an infusion reaction in another. CONCLUSIONS: Infliximab is a safe and effective treatment for IBD-associated pyoderma gangrenosum.     

Inflammatory bowel disease emergencies

Emergency complications of IBD are rare, but may be life-threatening, require surgery, and result in permanent end organ damage. The most common complications associated with UC are fulminant colitis, toxic megacolon, and bleeding. Each of these complications may resolve with aggressive medical therapy but often result in a total proctocolectomy. The most common complications associated with CD are abscesses and intestinal obstruction. Although initial treatment includes medical treatment, these Crohn's-related complications usually require a surgical intervention and intestinal resection. Finally, the most common extraintestinal manifestations that present as an emergency include thromboembolic events, ocular complications, and hepatobiliary disease. Some of these complications may parallel the course of the underlying disease and respond to IBD treatment, but thromboemboli, uveitis, and PSC do not. In the last decade there has been an explosion of knowledge and discovery into the pathogenesis of IBD. These findings have led to better and earlier treatment of IBD that it is hoped will alter the natural course of disease and prevent many of the complications outlined in this article.