Heterotaxia syndrome: the role of screening for intestinal rotation abnormalities.

BACKGROUND: Heterotaxia syndrome involves multiple anomalies, including cardiac malformations and intestinal rotation abnormalities. Most authors recommend routine radiological evaluation, with laparotomy and Ladd procedure if a rotation abnormality is found. AIMS: To determine if routine radiological screening is necessary, and if there is a group of children that can safely be managed expectantly. METHODS: Retrospective chart review of all children with heterotaxia syndrome from 1968 to 2002. RESULTS: Complete data were available for 177 patients. Twenty five (14%) had neonatal gastrointestinal symptoms (feeding intolerance, vomiting). Eleven of these had gastrointestinal contrast studies, of which seven were abnormal and led to surgery. Of the 152 asymptomatic neonates, nine had radiological screening and six of these were abnormal. Only one was thought to have a narrow based mesentery, but did not undergo surgery due to cardiac disease. There were no intestinal complications on follow up in this group. The other 143 asymptomatic children did not undergo radiological screening and were closely followed. Four subsequently developed gastrointestinal symptoms and had contrast studies; only one of these had malrotation and underwent a Ladd procedure. Of the remaining 139 patients who remained asymptomatic, 60 (43%) died of cardiac disease and none developed intestinal symptoms or complications related to malrotation on follow up. CONCLUSION: Asymptomatic children with heterotaxia syndrome have a low risk of adverse outcome related to intestinal rotation abnormalities. Routine screening may not be necessary as long as close follow up is done, and prompt investigation is performed for those that develop gastrointestinal symptomatology.

Extrathymic deletion of CD8+ alloreactive T cells in a transgenic T cell receptor model of neonatal tolerance.

BACKGROUND: Immunological tolerance to foreign antigen is most easily achieved during the neonatal period. Although deletion of T cells has been demonstrated in neonatal tolerance models in which donor and recipient express different MHC class II molecules, the requirement for deletion in MHC class I-disparate models is less clear. To address this issue, we used as recipient the T cell receptor (TCR) transgenic mouse (TgM) strain 2C in which the majority of CD8+ T cells express a single alpha/beta TCR alloreactive to H-2Ld, thus facilitating direct monitoring of the class I alloreactive population. METHODS: Newborn (less than 24 hr of age) 2C TgM received injections i.v.with syngeneic C57BL/6J (H-2b) (B6) or semiallogeneic (B6xDBA)F1 (H-2bd; H-2Ld+) splenocytes. Adults were subsequently analyzed in terms of tolerance, deletion of 2C+ T cells, and chimerism. RESULTS: The results showed that semiallogeneic-, but not syngeneic-, injected neonates were unresponsive as adults to H-2Ld-expressing target cells in vitro and the majority of these mice accepted H-2Ld+ skin grafts. Delaying the injection to 72 hr after birth or reducing the number of cells injected essentially abolished in vivo unresponsiveness in 2C recipients. Thus, the 2C TCR Tg model demonstrates the characteristics typical of neonatal tolerance. Injection of 2C neonates within 24 hr of birth with semiallogeneic versus syngeneic cells led to more than a 12-fold reduction of CD8+ 2C+ T cells in adult spleen and LNCs. In contrast, deletion of CD8+ 2C+ cells in adult thymus was not consistently observed. Based on MHC class II expression to distinguish donor (I-E+) and recipient (I-E-) cells, semiallogeneic-injected mice were chimeric in spleens and lymph nodes (LNs). CONCLUSIONS: These results demonstrate that neonatal MHC class I tolerance in the adult is associated with low level hematopoietic chimerism and extrathymic deletion of alloreactive CD8+ T cells.

CD8 expression up to the double-positive CD3(low/intermediate) stage of thymic differentiation is sufficient for development of peripheral functional cytotoxic T lymphocytes.

Control of CD8alpha transcription during development of alpha/beta T cell receptor (TCR) T lymphocytes is mediated by at least two distinct stage-specific cis-acting transcriptional mechanisms (i.e., enhancers). On the CD8alpha(-/-) knockout (KO) background, cis-mechanism I and cis-mechanism II together mediate appropriate stage- and sublineage-specific transgenic (Tg) CD8alpha expression and "rescue" development of peripheral CD8(+) single-positive (SP) cytotoxic T lymphocytes (CTLs). In contrast, on the wild-type (WT)/CD8(+/+) or CD8alpha(-/-)KO backgrounds, a CD8alpha Tg directed by cis-mechanism I alone is activated during the double negative [DN] to double positive [DP] transition and expressed up to the CD3(low/intermediate) DP stage but not in more mature DP or SP thymocytes or peripheral T cells. As loss of cis mechanism I activity occurs around the onset of positive selection, it is possible that events associated with TCR/major histocompatibility complex (MHC) interactions and selection are involved in initiating these changes in CD8alpha transcription. To examine this issue, phenotypic and functional studies were performed for thymocytes and T cells of CD8alpha(-/-) KO mice that expressed a CD8alpha Tg under control of cis-mechanism I only. Despite loss of CD8alpha expression at the DP CD3(low/intermediate) stage, increased populations of mature CD3(hi)CD4(-)CD8(-) thymocytes and CD3(+)CD4(-)CD8(-) peripheral T cells were detected. By several criteria, including MHC class I-restricted antigen recognition, these cells have at least partially undergone positive and negative selection. Therefore, initiation of selection and sublineage commitment are determined before loss of cis-mechanism I-mediated control of CD8alpha transcription. Further, CD8 expression beyond the CD3(low/intermediate) DP thymic stage is not essential for CTL development in vivo or function.

CD8+ T cells are necessary for recognition of allelic, but not locus-mismatched or xeno-, HLA class I transplantation antigens.

Although HLA transgenic mice (HLA TgM) could provide a powerful approach to investigate human MHC-specific T cell responsiveness, the extent to which these molecules are recognized by the mouse immune system remains unclear. We established TgM expressing HLA class I alleles A2, B7, or B27 in their fully native form (HLAnat) or as hybrid molecules (HLAhyb) of the HLA alpha1/alpha2 domains linked to the H-2Kb alpha3, transmembrane, and cytoplasmic domains (i.e., to maintain possible species-specific interactions). Comparison of each as xeno- (i.e., by non-TgM) vs allo- (i.e., by TgM carrying an alternate HLA allele) transplantation Ags revealed the following: 1) Although HLAhyb molecules induced stronger xeno-CD8+ T cell responses in vitro, additional effector mechanisms must be active in vivo because HLAnat skin grafts were rejected faster by non-TgM; 2) gene knockout recipients showed that xenorejection of HLAnat and, unexpectedly, HLAhyb grafts doesn't depend on CD8+ or CD4+ T cells or B cells; 3) each HLAhyb strain developed tolerance to "self" but rejected allele- (-B27 vs -B7) and locus- (-B vs -A) mismatched grafts, the former requiring CD8+ T cells, the latter by CD8+ T cell-independent mechanisms. The finding that recognition of xeno-HLAhyb does not require CD8+ T cells while recognition of the identical molecule in a strictly allo context does, demonstrates an alpha1/alpha2 domain-dependent difference in effector mechanism(s). Furthermore, the CD8+ T cell-independence of locus-mismatched rejection suggests the degree of similarity between self and non-self alpha1/alpha2 determines the effector mechanism(s) activated. The HLA Tg model provides a unique approach to characterize these mechanisms and develop tolerance protocols in the context of human transplantation Ags.

The effects of prebiopsy corticosteroid treatment on the diagnosis of mediastinal lymphoma.

BACKGROUND/PURPOSE: For children with probable mediastinal lymphoma and a high risk of cardiorespiratory morbidity, many centers recommend delaying the diagnostic biopsy for 24 to 48 hours while corticosteroids are administered to reduce tumor size and morbidity. This study was undertaken to determine the effect of preoperative steroid use on the accuracy of the pathological diagnosis and incidence of perioperative cardiorespiratory morbidity. METHODS: From 1988 to 1998, 86 children were treated for mediastinal lymphoma. Twenty-three received steroid before biopsy (study group) because of clinical evidence of respiratory compromise, and the remaining 63 served as controls. Clinical parameters, steroid use, and detailed pathological findings obtained at initial and subsequent biopsies were reviewed. Steroid treatment was considered to have had an adverse effect on the pathological diagnosis if (1) a definitive diagnosis was delayed more that 1 month, (2) a definitive diagnosis could not be made, or (3) the extent of disease could not be staged with certainty. RESULTS: Steroid treatment had an adverse effect on the pathological diagnosis in 5 of 23 (22%) children: 1 diagnostic delay, 3 failures of a definitive diagnosis, and 1 possible failure of staging. A definitive diagnosis was made in all control patients. Perioperative survival was 100% in both groups. At biopsy, only 3 children in the steroid treatment group and 2 children in the control group had moderate, nonfatal cardiorespiratory instability. Parameters of steroid use among children who had inaccurate pathological diagnoses or cardiorespiratory morbidity were not significantly different from those who did not. CONCLUSIONS: Steroid treatment before biopsy of mediastinal lymphoma may adversely affect the pathological accuracy or cause a delay in definitive diagnosis in a minority of cases. The dose and duration of steroid use was not related to outcome. Prebiopsy steroid appears to minimize the likelihood of cardiorespiratory morbidity in high-risk patients.