Electrophoretic characterization of the protein and glycoprotein content of purified Kurloff cell cytosol

Kurloff cell ultrastructure after combined formaldehyde-cetylpyridinium chloride fixation and high-iron diamine staining

This study deals with the ultrastructure of the chondroitin sulphate proteoglycans of the Kurloff body, a large lysosomal organelle that stains metachromatically with Toluidine Blue and which is present in Kurloff cells (a blood cell unique to the guinea pig). Splenic tissues were fixed with 1% cetylpyridinium chloride (CPC) added to 4% paraformaldehyde and examined either after Spicer's high-iron diamine staining for sulphated anionic sites followed by post-fixation with ferrocyanide-osmium tetroxide or after a simple post-fixation with ferrocyanide-osmium tetroxide. CPC-precipitated sulphated sites were preferentially located at the periphery of the Kurloff body but, unexpectedly, were absent in the central matrix. Although their electron opacity was lower, these anionic sites were readily observable in the absence of HID-staining after sole post-fixation by ferrocyanide-reduced osmium. CPC-precipitated sulphated anionic sites were either associated with the myelin figures or constituted unexpected structures. They contained (i) tightly-stacked lamellae, with a very regular 4 nm periodicity, and (ii) groups of 2, 3, 4 short dense lines with a 3-5 nm periodicity. By taking into account the susceptibility of these HID-reactive structures towards chondroitinase ABC, these different sulphated components were assumed to be related to the proteochondroitin-4-sulphate previously characterized as the only major sulphated glycoconjugate of the Kurloff cell. Their colocalization with phospholipidic structures was suggested following observation of sections treated by a chloroform-methanol mixture.

Glycoconjugates with Neu5Ac(alpha 2,6)Gal(beta 1,4)GlcNAc sequences: a selective lectin-histochemical property of Kurloff cells in guinea pig thymus

The Kurloff cell (KC), a natural killer lymphocyte, contains a large (10-microns diameter) periodic acid-Schiff (PAS)-positive lysosome-like inclusion body called the Kurloff body (KB), which exhibits strong acid phosphatase activity. The presence of Sambucus nigra agglutinin (SNA)-reactive Neu5Ac(alpha 2,6)-D-Gal/Gal-NAc(beta 1,4)GlcNAc oligosaccharide sequences and the absence of the corresponding Neu5Ac(alpha 2,3) Maackia amurensis agglutinin (MAA)-reactive sequence in the major 35-kDa N-glycosylproteins of the complex or hybrid type extracted from purified KC were established by Western-lectin-blotting of cytosolic extracts from purified KC. Moreover, these SNA-reactive sequences, or at least part of them, were shown to be borne by sialidase-sensitive KC acid isophosphatases. Thymic sections rich in KC, from estrogenized guinea pigs were examined by affino-histochemistry with these sialic acid-reactive lectins. The SNA-reactivity of thymic sections was quasi-exclusively confined to KC clusters, whereas the whole thymic section was negative for MAA. KC were not SNA-reactive following preincubation and incubation with 200 mM lactose. When submitted to enzymatic or mild chemical desialylation processes, the SNA-reactivity of the KC clusters was enhanced. The SNA-reactivity of KC clusters was completely abolished following prolonged chemical desialylation, whereas the PAS-positivity of KB remained unchanged. Even after a prolonged sialidase treatment, this SNA-reactivity was only reduced. Moreover, after both these desialylation processes, KC developed a heavier Ricinus communis agglutinin-reactivity, thus confirming the presence of penultimate Gal residues in their abundant SNA-reactive oligosaccharide sequences Neu5Ac(alpha 2,6)Gal(beta 1,4)GlcNAc. Such a selective lectin histochemical property provides a marker for detecting KC.

The major Kurloff cell glycoproteins: lectin affinities, glycosidase susceptibilities and relationship with the sialylated acid phosphatases of the Kurloff body

Urea-soluble fractions from purified Kurloff cells (KC) were analysed by affinoblotting. Lectin reactivities were quasi-exclusively confined to the 30-35 kDa major glycoproteins (mGPs) (responsible for the PAS positivity of the Kurloff body) with strong affinities for Canavalia ensiformis lectin, Phaseolus vulgaris erythroagglutinin and Sambucus nigra (SNA), Pisum sativum, Triticum vulgaris and Ulex europeus agglutinins. These data were consistent with the presence, among the KC mGPs, of large amounts of complex or hybrid N-glycosylproteins, in particular with Neu5Ac alpha 2,6Gal/GalNAc sequences, fucosyl residues and bisected residues. Their oligosaccharide sequences belong to more than one class, since some of these lectin reactivities had to be borne by distinct N-linked oligosaccharide chains. Before further analysis, KC mGPs were separated from other highly anionic glycoconjugates, by DEAE-cellulose chromatography. Their abundant potential RCA-binding sites masked by sialic acid were then revealed after neuraminidase (sialidase) or dilute acid pre-treatment. In remaining consistent with their lectin affinities, some KC mGPs were found to be PNGase F sensitive, while, either desialylated or not, they were all O-glycanase insensitive. Finally, by combined zymography and affinoblotting, the SNA-reactive fraction of KC mGPs was shown to correspond to denatured forms of the two zymographic size populations (190 kDa and 500 kDa) of KC acid phosphatases.

Presence of low affinity estrogen binding sites in guinea-pig Kurloff cells

Estrogen treatment of guinea-pig leads to an increase in the number of lymphoid cells containing Kurloff inclusions. The presence of estradiol binding sites in cytosolic extracts of Kurloff cells was investigated. We confirm here our previous inability to measure the typical type I estrogen receptor by using the classical dextran-charcoal procedure to separate bound and free ligand. We report now that low affinity estrogen binding sites (Kd approximately equal to 11 nM) can be detected when Kurloff cell extracts were fractionated on hydroxylapatite or Sephadex LH-20 after binding assay. Although the real function of these binding sites remains to be defined, the question arises again whether Kurloff cell represents a target cell for estrogens.

Cytochemical localization of arylsulfatase in guinea-pig Kurloff cells

Kurloff cells are mononuclear cells characterized by a large metachromatic and PAS-positive inclusion called the Kurloff body. Bone-marrow and spleen Kurloff cells were incubated with p-nitrocatechol sulfate as substrate and barium chloride as capturing agent for the ultracytochemical detection of the lysosomal marker enzyme, arylsulfatase. Enzymatic reaction product was consistently found as a single spot-like deposit confined to the rim of the Kurloff body. These results, and the previously described presence of other acid hydrolases and sulfated glycosamino++glycans, emphasize the similarities between the Kurloff body and lysosomes. Reaction product could also be found occasionally in segments of the rough endoplasmic reticulum but it was absent from the Golgi apparatus. This arylsulfatase activity could be related to the natural killer activity of Kurloff cells.

Kurloff cell proteoglycans. Evidence for de novo synthesis of chondroitin sulphate proteoglycans by purified Kurloff cells

This paper reports the first direct demonstration of de novo synthesis of chondroitin sulphate proteoglycans by Kurloff cells. This was achieved using highly purified splenic Kurloff cells labelled in vitro with [35S]sulphate and D-[U-3H]glucosamine. A single population of sulphated proteoglycans was observed after dissociative extraction, DEAE-cellulose chromatography, Sepharose CL 6B chromatography and fluorography after electrophoresis. These were large, highly anionic proteoglycans and were completely digested by chondroitinase AC or ABC. Moreover, glycosaminoglycan extracted from Kurloff cells had the electrophoretic mobility of control chondroitin sulphate.