Lysosomal acid hydrolases in lymphocytes of I-cell disease

B-cell-specific accumulation of inclusion bodies loaded with HLA class II molecules in patients with mucolipidosis II (I-cell disease)

BACKGROUND

I-cell disease is characterized by the presence of vacuole-like inclusions in lymphocytes. However, the nature and clinical significance of these inclusions have seldom been characterized. In this study, the authors tried to elucidate the distribution in different lymphocyte subpopulations, and the histological nature of the inclusions.

METHODS

Blood samples from three unrelated patients were analyzed. Lymphocyte subpopulations were separated using monoclonal antibodies conjugated to immunomagnetic beads. Cytochemical studies were performed using FITC-conjugated lectins. The expressions of surface and cytoplasmic class II molecules were analyzed by flow cytometry.

RESULTS

Virtually all B cells from the patients contained the inclusions. In contrast, CD4⁺ T cells, CD8⁺ T cells, natural killer cells, monocytes, or neutrophils did not contain the inclusions. Both fibroblasts and B cells from I-cell patients were stained intensely by multiple FITC-conjugated lectins with distinct binding profiles. The inclusions of B cells were stained intensely by fluorescence-conjugated antibodies against class II antigens.

CONCLUSIONS

Inclusions in I-cell disease reflect the accumulation of HLA class II molecules within B cells. These results suggest a potential role for N-acetylglucosamine-1-phosphotransferase in immune functions. Furthermore, the fact that only B cells contain the inclusions provides a novel diagnostic aid for the diagnosis of I-cell disease.

Plasma hyaluronidase activity in mucolipidoses II and III: marked differences from other lysosomal enzymes

A nearly pathognomonic finding of the lysosomal storage disorders mucolipidoses II and III is the marked increase of plasma lysosomal enzyme activities. The genetic lesion in ML II and III causes defective function of the enzyme UDP-GlcNAc:lysosomal enzyme N-acetylglucosamine-1-phosphotransferase. Defective function of this enzyme results in deficient phosphorylation of lysosomal enzyme asparagine-linked oligosaccharides and a consequent misrouting of many newly synthesized lysosomal enzymes. These enzymes are secreted from cells instead of being targeted to lysosomes, with resultant marked elevations of multiple lysosomal enzyme activities in plasma. We report here that plasma hyaluronidase activity, an endoglycosidase of presumably lysosomal origin, is not increased in the plasma from individuals with mucolipidoses II and III, unlike most lysosomal enzymes. Our data suggest the possibility that hyaluronidase is not targeted to lysosomes by a lysosomal enzyme phosphosmannosyl recognition mechanism. Alternatively, hyaluronidase activity may not be present in the cell type(s) responsible for the lysosomal enzyme hypersecretion in mucolipidoses II and III which, along with its deficiency in fibroblasts and leukocytes, would constitute an unusual tissue distribution of activity for a soluble lysosomal enzyme.

The activation of resting lymphocytes is accompanied by the biogenesis of lysosomal organelles

The degradative activity of lymphocytes plays by important role in a number of essential immune functions. In the present study we have examined how the activation of resting lymphocytes, by the mitogen concanavalin A (Con A), affects three major components of the lysosomal compartment: the lysosomal enzyme beta-glucuronidase (Gus); an integral lysosomal membrane protein (LAMP-1); and the mannose 6-phosphate receptor (MPR) which directs lymphocyte enzyme transport. Resting T cells were found to contain only very low levels of these proteins, but they were actively synthesized by, and far more abundant in, stimulated lymphoblasts. Although the lysosomal antigens did not have a distinct cytoplasmic localization in the resting lymphocytes, in the activated T lymphoblasts they were present in several highly developed intracellular structures, including the rough endoplasmic reticulum and the Golgi complex. Furthermore, in these latter cells Gus was also found to be accumulated within the lumen of large vesicles which we characterized as lysosomes by the presence of LAMP-1 at the periphery and by the absence of MPR. Subcellular fractionation confirmed that these organelles were present in the activated lymphocytes only, and not in the resting T cells. Our results demonstrate that lymphocyte activation is accompanied by the synthesis of the enzymic and structural components of the lysosomal compartment which are sorted and assembled into distinct organelles in the activated cell.

I-cell disease: clinical studies of 21 Japanese cases

Clinical pictures of 21 cases with I-cell disease patients, 12 males and 9 females, were analyzed. Characteristic coarse facial features and shortness of stature were observed in all cases. In general, the motor development was found to be more severely retarded than the mental development of the patients. Rather little involvement of the nervous system seemed to cause somewhat acceptable mental development in some cases, and also cause the absence of epileptic seizures in all cases. Involvement of the cardiovascular system, especially progressive hypertrophic cardiomyopathy, could be highly responsible for frequent sudden death of I-cell disease patients.

Effects of mitogenic stimulation of lymphocytes on lysosomal enzyme activity

Changes in the activities of several lysosomal enzymes were studied during transformation of mouse spleen cells in vitro. The activity of beta-glucuronidase increased during culture in the presence of T or B-cell mitogens, and lymphoblasts contained higher levels of activity than did small, non-transformed lymphocytes. Moreover, lymphoblasts in well-transformed cultures had higher activities than those in poorly-transformed cultures. The activities of other lysosomal enzymes (N-acetyl-beta-glucosaminidase, alpha-mannosidase, beta-glucosidase) also increased during mitogenic stimulation, but each at different rates, although aryl sulphatase was unaffected. Such differences may be of importance when lymphocytes are used for diagnosis of inherited lysosomal deficiency diseases.

beta-Glucuronidase in gastric aspirate after oral cimetidine in the diagnosis of carcinoma of the stomach

The activity of beta-glucuronidase was studied in the gastric aspirate from normal individuals, cases of duodenal ulcer with pyloric stenosis and carcinoma of the stomach. The optimum pH for the activity of this enzyme in the gastric aspirate is 4.0 to 5.5. Cimetidine, a H2-receptor antagonist, was administered orally to obtain the optimum pH for the enzyme activity, when the pH of the gastric aspirate was less than 4.0. It is observed that the enzyme activity in cases of carcinoma of the stomach is markedly elevated (p less than 0.01), when compared with other cases in this study. It is suggested that the elevated enzyme activity in the gastric aspirate could be used as a biochemical marker in the diagnosis of carcinoma of the stomach.

The mucolipidoses: identification by abnormal electrophoretic patterns of lysosomal hydrolases

The human mucolipidoses (ML) are characterized by abnormal activities and abnormal electrophoretic patterns of fibroblast lysosomal hydrolases. These altered mobility patterns can be used to confirm the clinical diagnosis of the four mucolipidoses. The mobility patterns of one nonlysosomal and seven lysosomal enzymes were tested in fibroblasts from two ML I (sialidosis type 2, infantile), fifteen ML II (I-cell disease), eight ML III (pseudohurler polydystrophy), and one ML IV patients. A single sialidosis type 2, juvenile, line was also examined. Characteristic mobility patterns were found which identify each of the four mucolipidoses. Both the ML I and sialidosis type 2 juvenile lines displayed anodal mobility patterns, but distinct differences between the two disorders were observed. Lysosomal hydrolases from ML II lines demonstrated reduced activities or had altered mobilities. Differing electrophoretic patterns demonstrated the presence of at least two groups within the clinical phenotype diagnosed as ML II, indicating heterogeneity. The ML III lines showed normal electrophoretic patterns for most lysosomal hydrolases. The ML IV line expressed normal mobilities for every enzyme studied, with a single exception. The electrophoretic patterns of only beta-hexosaminidase, acid phosphatase-2, alpha-galactosidase, and esterase A4 were sufficient to identify and distinguish the different mucolipidosis types. Electrophoretic variation was also seen in liver but not kidney extracts from three ML II patients. beta-Hexosaminidase and alpha-mannosidase B secreted into the medium by ML II and ML III fibroblasts had mobility patterns different from normal and from their intracellular patterns. These data suggest that the mucolipidoses are genetically distinct with heterogeneity within them.