Differences in the surface proteins of mouse B and T cells

Construction and properties of new Lyt-congenic strains and anti-Lyt-2.2 and anti-Lyt-3.1 monoclonal antibodies

Hybridomas producing mouse monoclonal IgM antibodies specific for Lyt-2.2 and Lyt-3.1 T-cell surface alloantigens have been constructed. Cytotoxic titers of ascites fluids were found to be 10(-6) or greater and no lysis of thymocytes of congenic strains bearing the alternative allele was observed at the lowest dilutions tested (1:2). The anti-Lyt-2.2 monoclonal antibody (HO-2.2) specifically precipiated from extracts of Lyt-2.2-positive thymocytes molecular species indistinguishable from those precipitated by conventional anti-Lyt-2.2 sera. However, by immunoprecipitation criteria (though not by cytotoxicity), the anti-Lyt-3.1 antibody (HO-3.1) demonstrated some cross-reactivity with similar molecular species from Lyt-3.1-negative thymocytes. In addition, three new strains of mice differing from existing strains in the region of the Lyt-2 and Lyt-3 loci have been constructed. They are: C.C58-Lyt-2a, Lyt-3a and C.AKR-Lyt-2a, Lyt-3a, congenic with Balb/cAn and bearing Lyt-2a and Lyt-3a alleles of C58/J and AKR/J, respectively; and AKR.C-Lyt-2b, Lyt-3b congenic with AKR/J and bearing the Lyt-2b and Lyt-3b alleles of Balb/cJ.

Identification, isolation, and culture of intestinal epithelial stem cells from murine intestine

The study of adult stem cell populations provides insight into the mechanisms that regulate tissue maintenance in normal physiology and many disease states. With an impressive rate of epithelial renewal driven by a pool of multipotent stem cells, the intestine is a particularly advantageous model system for the study of adult stem cells. Until recently, the isolation and in vitro study of intestinal epithelial stem cells (IESCs) was not possible due to the lack of biomarkers and culture techniques. However, advances in molecular characterization and culture of IESCs have made in vitro studies on this cell type amenable to most laboratories. The methods described in this chapter will allow the investigator to adapt newly established techniques toward downstream analysis of IESCs in vitro.

A T-cell marker in mouse fibroblast x T-lymphocyte somatic cell hybrids

Continuous hybrid cell lines have been generated by the fusion of allogeneically primed murine T lymphocytes with mouse L-cell-derived fibroblasts of the line 613. The resulting hybrid clones express one or more T-cell-specific surface components identifiable by radioiodination of intact cells followed by NP-40 solubilization of membrane proteins and sodium dodecyl sulfate polyacrylamide gel electrophoresis. These markers are stably expressed by the hybrid lines after several months of passage.

Differential ability of isolated H-2 Kb subsets to serve as TCR ligands for allo-specific CTL clones: potential role for N-linked glycosylation

It is not known whether all forms of cell surface peptide-class I complexes, when bound with relevant peptide antigen, are recognized by T cells. We demonstrate herein that two distinct subsets of the murine H-2 Kb molecule can be separately isolated from H-2b-expressing cell lines using Y3 mAb immunoaffinity chromatography. Although both isolated Kb subsets were found to be strongly reactive with Y3 mAb by ELISA, one Kb subset is S19.8 mAb reactive (Ly-m11+Kb subset) and exhibits low reactivity with the M1/42 antibody, while the other subset is negative for the Ly-m11 epitope and highly reactive with the M1/42 antibody (M1/42high Kb subset). More importantly, whereas the M1/42high Kb subset is a very effective ligand for both TCR and CD8, the Ly-m11+ Kb subset could only function as a CD8 ligand, as determined in allo-specific CD8+ CTL clone adhesion and degranulation assays. Peptides acid-eluted from both Kb subsets sensitized Kb-transfected T2 cells expressing "peptide empty" Kb for lysis to a similar extent by allo-CTL clones, indicating that relevant endogenous peptide antigens are not limiting in the Ly-m11+ Kb subset. The major distinction identified between the two Kb subsets is that they differ substantially in their degree of N-linked glycosylation, with the Ly-m11+ subset containing Kb molecules with larger and more complex carbohydrate modifications than the M1/42high subset. The differences in glycosylation may explain the functional differences observed between the two Kb subsets. It is therefore possible that some forms of glycosylation on class I molecules interfere with TCR recognition and may limit CD8+ T cell responses, perhaps under circumstances where peptide antigen is limiting.

Tyrosine phosphorylation of CD45 phosphotyrosine phosphatase by p50csk kinase creates a binding site for p56lck tyrosine kinase and activates the phosphatase

Src family protein tyrosine kinases (PTKs) play an essential role in antigen receptor-initiated lymphocyte activation. Their activity is largely regulated by a negative regulatory tyrosine which is a substrate for the activating action of the CD45 phosphotyrosine phosphatase (PTPase) or, conversely, the suppressing action of the cytosolic p50csk PTK. Here we report that CD45 was phosphorylated by p50csk on two tyrosine residues, one of them identified as Tyr-1193. This residue was not phosphorylated by T-cell PTKs p56lck and p59fyn. Tyr-1193 was phosphorylated in intact T cells, and phosphorylation increased upon treatment with PTPase inhibitors, indicating that this tyrosine is a target for a constitutively active PTK. Cotransfection of CD45 and csk into COS-1 cells caused tyrosine phosphorylation of CD45 in the intact cells. Tyrosine-phosphorylated CD45 bound p56lck through the SH2 domain of the kinase. Finally, p50csk-mediated phosphorylation of CD45 caused a severalfold increase in its PTPase activity. Our results show that direct tyrosine phosphorylation of CD45 can affect its activity and association with Src family PTKs and that this phosphorylation could be mediated by p50csk. If this is also true in the intact cells, it adds a new dimension to the physiological function of p50csk in T lymphocytes.

Tyrosine phosphorylation of CD45 phosphotyrosine phosphatase by p50csk kinase creates a binding site for p56lck tyrosine kinase and activates the phosphatase

Src family protein tyrosine kinases (PTKs) play an essential role in antigen receptor-initiated lymphocyte activation. Their activity is largely regulated by a negative regulatory tyrosine which is a substrate for the activating action of the CD45 phosphotyrosine phosphatase (PTPase) or, conversely, the suppressing action of the cytosolic p50csk PTK. Here we report that CD45 was phosphorylated by p50csk on two tyrosine residues, one of them identified as Tyr-1193. This residue was not phosphorylated by T-cell PTKs p56lck and p59fyn. Tyr-1193 was phosphorylated in intact T cells, and phosphorylation increased upon treatment with PTPase inhibitors, indicating that this tyrosine is a target for a constitutively active PTK. Cotransfection of CD45 and csk into COS-1 cells caused tyrosine phosphorylation of CD45 in the intact cells. Tyrosine-phosphorylated CD45 bound p56lck through the SH2 domain of the kinase. Finally, p50csk-mediated phosphorylation of CD45 caused a severalfold increase in its PTPase activity. Our results show that direct tyrosine phosphorylation of CD45 can affect its activity and association with Src family PTKs and that this phosphorylation could be mediated by p50csk. If this is also true in the intact cells, it adds a new dimension to the physiological function of p50csk in T lymphocytes.

Identification of a putative receptor for subgroup A feline leukemia virus on feline T cells

Retrovirus infection is initiated by the binding of virus envelope glycoprotein to a receptor molecule present on cell membranes. To characterize a receptor for feline leukemia virus (FeLV), we extensively purified the viral envelope glycoprotein, gp70, from culture supernatants of FeLV-61E (subgroup A)-infected cells by immunoaffinity chromatography. Binding of purified 125I-labeled gp70 to the feline T-cell line 3201 was specific and saturable, and Scatchard analysis revealed a single class of receptor binding sites with an average number of 1.6 x 10(5) receptors per cell and an apparent affinity constant (Ka) of 1.15 x 10(9) M-1. Cross-linking experiments identified a putative gp70-receptor complex of 135 to 140 kDa. Similarly, coprecipitation of 125I-labeled cell surface proteins with purified gp70 and a neutralizing but noninterfering anti-gp70 monoclonal antibody revealed a single cell surface protein of approximately 70 kDa. These results indicate that FeLV-A binds to feline T cells via a 70-kDa cell surface protein, its presumptive receptor.

Intimate association of Thy-1 and the T-cell antigen receptor with the CD45 tyrosine phosphatase

Immunoprecipitation of Thy-1 from Triton X-100 detergent lysates of surface-iodinated and chemically cross-linked T cells precipitated at least five major and discrete bands. Four of these bands were identified as Thy-1, CD45 (a transmembrane tyrosine phosphatase), a major histocompatibility complex-encoded class I molecule, and beta 2-microglobulin. Similar analyses revealed that CD45 was coprecipitated from lysates of cross-linker-treated cells by antibodies to the T-cell antigen receptor (TCR). The same pattern of coprecipitated bands was observed when digitonin was used to lyse untreated cells. Immunoprecipitation of Thy-1 or the TCR from lysates of cross-linked T cells precipitated CD45 tyrosine phosphatase activity. Calculations based upon the amounts of coprecipitated enzymatic activity or TCR zeta chain indicate that a substantial fraction of Thy-1 and TCR complexes can be cross-linked to CD45. These data support a model in which the dependence of Thy-1 signaling on TCR coexpression is due to their common interaction with a tyrosine phosphatase and provide a possible structural basis for the influence of CD45 on TCR-mediated signaling.

p180, a novel recycling transmembrane glycoprotein with restricted cell type expression

A 180-kilodalton (kDa) protein (p180) was identified among the antigens for a panel of monoclonal antibodies raised against human fibroblast cell surface proteins. Binding studies with 125I-Fab' fragments of an anti-p180 monoclonal antibody demonstrated that 10 to 30% of p180 was located on the plasma membrane and that the remaining 70 to 90% was on intracellular membranes. p180 was rapidly internalized from the cell surface at 37 degrees C, and kinetic analyses indicated that this was a constitutive process followed by the recycling of p180 back to the plasma membrane. Morphological studies demonstrated that on the cell surface p180 was concentrated in coated pits, whereas inside the cell it was found in endosomes as suggested by its colocalization with the transferrin receptor. Immunoblot analysis with a polyclonal antiserum raised against purified human protein showed that p180 has a restricted distribution with expression at high levels in fibroblast cultures and in tissues containing cells of mesodermal origin. A biochemical characterization of p180 showed it to be a transmembrane glycoprotein with an extracellular domain, which consists of approximately 30 kDa of complex oligosaccharides attached to at least 45 kDa of the protein core. The cytoplasmic domain of p180 was found to contain a serine residue(s) that was phosphorylated both in vivo and in vitro by activated protein kinase C. p180 was purified by subjecting solubilized membrane proteins from a human osteosarcoma cell line to immunoaffinity chromatography and gel filtration. The N-terminal sequence information obtained from the purified protein showed no homology to other known proteins. It was concluded that p180 may be a novel recycling receptor which is highly restricted in its expression to fibroblastlike cells.

RT7-defined alloantigens in rats are part of the leucocyte common antigen family

Haemopoietic cells carry a variety of cell-surface molecules, some of which are known to have allotypic variation. In rats, the RT7 alloantigenic system has been well documented using alloantisera. We have produced the first mouse hybridoma cell line secreting an antibody, HIS41, which binds to leucocytes of rat strains carrying the RT7.2 but not the RT7.1 determinant. An IgG2b isotype switch variant (HIS41.2b) of the original HIS41 (IgG1 isotype) was also made. HIS41 showed a clear and discrete binding in immunofluorescent and histological experiments and has already been used in several studies on haemopoietic cell turnover and differentiation employing PVG rats congenic for RT7. The present study addresses the question of whether the RT7 gene products are members of the L-CA family, which has been a matter of controversy over the last decade. When using HIS41 for the analysis of tissue distribution and molecular weight of RT7 gene products, a strong similarity was evident with the data reported for the L-CA detected by MRC OX-1 and MRC OX-30. These two MoAb have been reported to bind to all members of the L-CA family. All haemopoietic cells, excluding erythrocytes and the more mature stages of erythropoiesis, stained with HIS41. The molecular weights of HIS41 binding molecules on thymocytes and peripheral T cells were comparable to the L-CA precipitated by MRC OX-1. Capping and sequential immunoprecipitation studies indicated that HIS41 and MRC OX-30-binding molecules were identical. MRC OX-1, however, appeared to bind only a subset of these molecules. Thus, our study confirms the identity of RT7.2 gene products and L-CA. It also revealed a difference between MRC OX-1 and MRC OX-30 not noticed previously.

p180, a novel recycling transmembrane glycoprotein with restricted cell type expression

A 180-kilodalton (kDa) protein (p180) was identified among the antigens for a panel of monoclonal antibodies raised against human fibroblast cell surface proteins. Binding studies with 125I-Fab' fragments of an anti-p180 monoclonal antibody demonstrated that 10 to 30% of p180 was located on the plasma membrane and that the remaining 70 to 90% was on intracellular membranes. p180 was rapidly internalized from the cell surface at 37 degrees C, and kinetic analyses indicated that this was a constitutive process followed by the recycling of p180 back to the plasma membrane. Morphological studies demonstrated that on the cell surface p180 was concentrated in coated pits, whereas inside the cell it was found in endosomes as suggested by its colocalization with the transferrin receptor. Immunoblot analysis with a polyclonal antiserum raised against purified human protein showed that p180 has a restricted distribution with expression at high levels in fibroblast cultures and in tissues containing cells of mesodermal origin. A biochemical characterization of p180 showed it to be a transmembrane glycoprotein with an extracellular domain, which consists of approximately 30 kDa of complex oligosaccharides attached to at least 45 kDa of the protein core. The cytoplasmic domain of p180 was found to contain a serine residue(s) that was phosphorylated both in vivo and in vitro by activated protein kinase C. p180 was purified by subjecting solubilized membrane proteins from a human osteosarcoma cell line to immunoaffinity chromatography and gel filtration. The N-terminal sequence information obtained from the purified protein showed no homology to other known proteins. It was concluded that p180 may be a novel recycling receptor which is highly restricted in its expression to fibroblastlike cells.

The LY-1 gene expression in murine hybridomas producing autoantibodies

Studies presented here demonstrate the expression of the Ly-1 gene and the detection of the Ly-1 cytodifferentiation antigen in murine hybridomas producing autoantibodies. We examined the transcription of the Ly-1 gene in thymocytes and 140 hybridomas producing autoantibodies of various specificities which were obtained from normal and autoimmune disease prone mouse strains. As previously demonstrated thymocytes stain brightly for Ly-1 by immunofluorescence and express Ly-1 transcripts. In our panel of hybridomas producing autoantibodies Ly-1 transcripts were detected in 31 (45%) out of 69 NZB hybridomas and 7 (88%) out of 8 viable motheaten hybridomas. S1 nuclease protection experiments showed that Ly-1 transcripts detected in thymocytes and B cells are the product of the same gene. The B cell transcripts are functional since immunofluorescence and Western data presented here detected the Ly-1 protein in hybridomas cells which were found to transcribe the Ly-1 gene. Interestingly a polymorphic transcription of the Ly-1 gene was observed in B cells and B cell hybridomas as compared to thymocytes. Our results obtained in the hybridoma system firmly establish a major contribution of the Ly-1 B cell subset to the production of DNA specific autoantibodies and a smaller contribution to the production of rheumatoid factors and "natural", multispecific autoantibodies.

The surface of dendritic cells in the mouse as studied with monoclonal antibodies

A family of dendritic cells has been identified in situ and in vitro by microscopy and immunolabeling. The members of this family include the dendritic cells isolated from lymphoid organs, Langerhans cells [LC] of the epidermis, veiled cells in afferent lymph, and interdigitating cells [IDC] in the T-cell areas. Some common features to all members of the family are high levels of MHC class II antigens, a lack of most B and T cell markers, and an absence or low levels of macrophage/granulocyte antigens. This review summarizes the markers of mouse dendritic cells as assessed by a panel of monoclonal antibodies, and stresses a few recent findings. 1) In spleen, there are two populations of dendritic cells. More than 75% of isolated cells are 33D1+, NLDC145-, and J11d-, while the remainder have the reciprocal phenotype and thus share the NLDC145 antigen of IDC. Thymic dendritic cells, released by collagenase digestion, and epidermal LC also are 33D1-, NLDC145+, J11d+. 2) When epidermal LC are placed in culture, there are changes in cell function and phenotype. There is a decrease in Fc gamma receptors and the F4/80 macrophage antigen, an increase in class I and II MHC products and p55 IL-2 receptors, and persistence of the NLDC145 IDC antigen. The cultured LC thereby resembles the IDC. 3) A new antibody N418 shows that dendritic cells express the p150/90 member of the leukocyte beta 2 integrin family. Immunolabeling of tissue sections of spleen indicates that N418+ dendritic cells not only are present in the periarterial sheaths, the location of IDC, but also in "nests" at the periphery of the T area where 33D1 has been found. The peripheral collections interrupt the marginal zone of macrophages that separates white and red pulp, and places the dendritic cells in the path of T cells as they move through the white pulp. Therefore the members of the dendritic cell family have important markers in common, as well as differences that are associated with state of immunologic function and location.

The secreted form of the Alzheimer's amyloid precursor protein with the Kunitz domain is protease nexin-II

The A4 protein (or beta-protein) is a 42- or 43-amino-acid peptide present in the extracellular neuritic plaques in Alzheimer's disease and is derived from a membrane-bound amyloid protein precursor (APP). Three forms of APP have been described and are referred to as APP695, APP751 and APP770, reflecting the number of amino acids encoded for by their respective complementary DNAs. The two larger APPs contain a 57-amino-acid insert with striking homology to the Kunitz family of protease inhibitors. Here we report that the deduced amino-terminal sequence of APP is identical to the sequence of a cell-secreted protease inhibitor, protease nexin-II (PN-II). To confirm this finding, APP751 and APP695 cDNAs were over-expressed in the human 293 cell line, and the secreted N-terminal extracellular domains of these APPs were purified to near homogeneity from the tissue-culture medium. The relative molecular mass and high-affinity binding to dextran sulphate of secreted APP751 were consistent with that of PN-II. Functionally, secreted APP751 formed stable, non-covalent, inhibitory complexes with trypsin. Secreted APP695 did not form complexes with trypsin. We conclude that the secreted form of APP with the Kunitz protease inhibitor domain is PN-II.

The extra segments of sequence in rat leucocyte common antigen (L-CA) are derived by alternative splicing of only three exons and show extensive O-linked glycosylation

The leucocyte common antigen (L-CA, CD45, or T200) consists of a family of heavily glycosylated glycoproteins of apparent Mr 180,000-240,000 found at the surface of leucocytes but not other cell types. Populations of lymphocytes express forms that differ in antigenicity, apparent Mr, and glycosylation. Some of this heterogeneity is due to polypeptide differences caused by the insertion of up to three different segments of sequence near the NH2-terminus. We report the complete sequence of the region of the rat L-CA gene encoding the extra segments. Analysis of this sequence showed that each segment was encoded by an exon but no further exons could be identified, implying that the polypeptide heterogeneity is solely due to selection from these three exons by alternative splicing. Amino acid sequencing of glycopeptides prepared from the largest forms of L-CA indicated extensive O-linked glycosylation in at least one of the extra segments.

CD45 regulates signal transduction and lymphocyte activation by specific association with receptor molecules on T or B cells

Evidence is presented that the leukocyte common antigen CD45 can regulate both signal transduction by lymphocyte receptor molecules and T- and B-cell proliferation in a manner dependent on specific interactions between these receptors on the cell surface. Formation of homoaggregates of CD3, CD2, or CD28 on the surface of T cells induced by crosslinking with monoclonal antibodies (mAbs) results in an increase in cytoplasmic free calcium concentration ([Ca2+]i). This increase in [Ca2+]i was abolished when these receptors were crosslinked to CD45 on the cell surface. In contrast, the increase in [Ca2+]i induced by formation of homoaggregates of CD4 was strongly amplified when CD4 was coupled to CD45. T-cell proliferation initiated by immobilized anti-CD3 was inhibited by anti-CD45 or anti-CD45R when immobilized on the same surface, but not when in solution. Similarly, proliferation after stimulation of the CD2 and CD28 receptors was inhibited when a CD45 mAb was crosslinked to either CD2 or CD28 mAbs, but not when a CD45-specific mAb was bound to the cell surface separately. In B cells, the increase in [Ca2+]i and resulting proliferation induced by crosslinking either the CD19 or Bgp95 receptors was inhibited by coupling these molecules to CD45. Thus, CD45 appears to modify other cellular receptors functionally when brought into close physical association with them. The homology of the CD45 conserved cytoplasmic domains with a major human placental protein tyrosine phosphatase suggests that the effects of CD45 described here result from alterations in the phosphorylation state of tyrosyl residues in membrane-associated proteins.

Expression of B220 antigen on an interleukin 4- and interleukin 5-producing T-cell line

The murine T-cell line 2.19, originally used for cloning of interleukin 4 (IL-4) and IL-5, was analysed for surface marker characteristics using monoclonal antibodies and a FACS-4 analyser and found to be positive for the B220 antigen. Thus, this lymphokine-producing cell with characteristic T-cell markers expresses an antigen earlier thought to be specific for B cells. With two-colour fluorescence it was found that a small fraction (2-4%) of Thy 1+ spleen cells from normal CBA mice were also positive for B220.

CD45R gives immunofluorescence and transduces signals on mouse T cells

The expression of CD45R on mouse T cells has been studied. This antigen is expressed on the two higher molecular weight bands of CD45 (or T200) and in mouse it is currently used as a marker of B cells (B220). Here we confirm that CD45R is expressed on some mouse T cell clones. We show that a small but measurable proportion of mouse spleen and peripheral blood lymphocyte T cells gives positive immunofluorescence with B220. Also CD45R-specific antibodies increase the proliferation response to phytohemagglutinin up to 3-fold, thus confirming that CD45R molecules transduce a signal into mouse T cells.

Brain surface invasion and metastasis of murine malignant melanoma variants

Mouse B16 melanoma sublines were selected sequentially for their abilities to colonize brain meninges and leptomeninges of C57BL/6 mice. After 14 selections subline B16-B14b was established that formed significantly more brain tumor colonies than the parental B16 line. Examination of brains at various times after intravenous or intra-arterial injection of B16 cells by electron microscopy revealed that B14b melanoma cells lodged in small brain blood vessels, proliferated and invaded through vessel walls into brain parenchyma and also along small blood vessels at perivascular sites. Invasion into brain parenchyma was characterized by extension of melanoma cell filopodia resulting in fragmentation and sometimes enfulgment of glial and neural cells. Analysis of cell surface proteins of B16 melanoma sublines revealed increased exposure of a Mr approximately 90,000 glycoprotein on the high brain-colonizing cells. Antibodies against the Mr approximately 90,000 glycoprotein reacted with a variety of human melanoma cell lines and with some fetal and adult tissues, indicating that this melanoma-associated component is not species-, tumor- or tissue-specific. The glycoprotein could be a cell surface receptor important in the survival and growth properties of melanoma cells in brain microenvironments.

Alternative use of 5' exons in the specification of Ly-5 isoforms distinguishing hematopoietic cell lineages

Previous inferences that Ly-5 glycoprotein isoforms of murine hematopoietic cells are generated by alternative splicing of primary transcripts of a single Ly-5 gene are supported by the present study. A cDNA library was prepared from B cells by extension from primer representing a known T-cell cDNA sequence. Three different Ly-5 clones from this library included sequences missing in T-cell cDNA clones. From the constitution of cDNA clones and of the Ly-5 gene, and from S1 nuclease mapping, it is concluded that at least two exons, provisionally numbered Ex-6(B) and Ex-7(B), in the 5'-proximal region are mainly represented in mRNA of the B-cell lines examined but not of the T-cell lines examined. Also, exons 1 and 2 appear to be used alternatively in different species of B-cell mRNA and probably also in different species of T-cell mRNA.

B-cell variant of mouse T200 (Ly-5): evidence for alternative mRNA splicing

The complete cDNA sequence of mouse T200 glycoprotein from the pre-B-cell line 70Z/3 has been determined. The deduced protein sequence differs from that previously reported for a T-cell form of the molecule [Saga, Y., Tung, J.-S., Shen, F.-W. & Boyse, E. A. (1986) Proc. Natl. Acad. Sci. USA 83, 6940-6944] by the insertion of 139 amino acid residues in the amino-terminal region of the molecule. RNA transfer blotting using a cDNA probe encoding this sequence established that the predominant T200 mRNA species from B cells and cytotoxic T-cell clones but not T-helper cell clones or thymocytes contain all or part of the insert. Overlapping genomic clones of murine T200 were isolated and analysis of the intron-exon structure at the 5' end of the gene provides evidence that variants of T200 glycoprotein are generated by alternative mRNA splicing.

Structural variants of human T200 glycoprotein (leukocyte-common antigen)

Structural variation in the primary structure of human T200 glycoprotein has been detected. Three cDNA variants have been characterized each of which encode T200 molecules that differ in size as a result of sequence differences in their amino-terminal regions. The largest form of the molecule is distinguished from the smallest by an insert of 161 amino acids, after the first eight amino-terminal residues. The other variant has an insert at the same location of 47 amino acids identical to residues 75-121 in the larger insert. Both extra domains are rich in serine and threonine residues and are likely to display multiple O-linked oligosaccharides. These structural variants which probably arise by cell-type-specific alternative splicing provide a molecular basis for the previously observed structural and antigenic heterogeneity of T200 glycoprotein. In addition to the variable amino-terminal region, the external domain of human T200 glycoprotein consists of a second cysteine-rich region of about 400 amino acids, a single transmembrane-spanning region and a large cytoplasmic domain of 707 amino acids shared by all of the structural variants and highly conserved between species. The gene encoding human T200 is located on the long arm of chromosome 1.

Lymphocyte specific heterogeneity in the rat leucocyte common antigen (T200) is due to differences in polypeptide sequences near the NH2-terminus

The leucocyte-common antigen (L-CA, T200 or CD45) consists of a family of heavily glycosylated glycoproteins of apparent Mr 180,000-240,000 which are restricted to lymphoid and myeloid cells. Forms of L-CA which differ in their apparent Mr, antigenicity and glycosylation are expressed on different lymphocyte types. One specific antigenic determinant called MRC OX-22 is of particular interest because it distinguishes two sets of T helper cells that have different functions. From the sequence of different L-CA cDNA clones we now conclude that there is sequence heterogeneity such that at least four forms of L-CA exist with sequences in the range 1118-1250 amino acids. All the sequence variation occurs at a point starting 6 residues from the NH2-terminus and the last 1112 residues of all forms are identical. Two of the variants can be directly related to the antigenic variation because they include sequence that was determined for a peptide that carries the MRC OX-22 determinant. Analysis of glycopeptides from thymocyte L-CA identified only one non-glycosylated position out of 14 possible N-glycosylation sites and established that all O-glycosylation was within the first 32 amino acids. The extra protein sequence in the longer forms was also suggestive of extensive O-glycosylation.

A new epitope of the T200 molecule family defined by the 3A35 monoclonal antibody and expressed by macrophages and activated T lymphocytes

A monoclonal antibody (mAb), 3A35, produced against mouse macrophages (M phi) was found to react against certain activated T cells. This mAb, a rat IgM, resulted from a cell fusion between a mouse plasmacytoma and rat lymphocytes immunized against mouse M phi. It bound more avidly to activated than to resident M phi. It did not react against B cells and resting T lymphocytes but recognized certain dividing T cells like EL4 lymphoma, concanavalin A-activated and interleukin 2-expanded spleen cells, and helper T cell hybridomas. By contrast, other T lymphocyte-derived cell lines such as YAC-1 and CTLL2 were unreactive. No clear relationship was found between the binding of 3A35 to cells and the expression of L3T4 and Lyt-2 antigens. The specific stimulation of T cell clones with antigen rapidly induced a strong reactivity with 3A35 mAb which declined thereafter to a low (helper clones) or non-reactivity (cytotoxic clones) after 10 days of culture. Immunoprecipitation experiments, performed with M phi derived from bone marrow cell cultures, surface iodinated with 125I or metabolically labeled with [35S]methionine, showed that 3A35 bound to a 200-kDa molecule, shifting to 175 kDa under reducing conditions. In peritoneal M phi activated in vivo, in addition to the 175-kDa band, new bands migrating at 140, 120 and 85 kDa were identified by 3A35 and could be absorbed on a commercial anti-T200 mAb bound to Sepharose beads. After strengthening the cell binding of 3A35 to EL4 lymphoma cells by a cross-linking agent, only a 85-kDa molecule was immunoprecipitated. Thus, 3A35 identifies a new epitope of the T200 molecule family which is expressed on M phi and activated T cells.

Structural studies of T200 glycoprotein and the IL-2 receptor

Immunological analysis of the cell surface of hematopoietic cells has led to the identification of many different cell membrane molecules, some of which have well-defined functions as receptors. In general, however, the role of most lymphocyte cell surface molecules remains ill-defined even in cases in which antibody inhibition studies have given some insight into the biological processes in which they participate. Here we describe molecular and biochemical studies of T200 glycoprotein (leukocyte-common antigen) and the IL-2 receptor which illustrate the kinds of approaches that can be currently used to characterize individual molecules. T200 glycoprotein is a large Mr glycoprotein found exclusively on leukocytes. However, the exact Mr varies in a cell-type-specific fashion and this property is conserved between different species. Comparison of the rat, mouse and human cDNA sequences show that the large cytoplasmic portion of the molecule is well-conserved, approximately 90%, whereas the exterior portion is only about 50% homologous. Cell-type-specific differences in the primary sequence of the molecule have been identified in the N-terminal portion of the molecules. In contrast to T200, the function of the IL-2 receptor is well-known. The interaction of IL-2 with its receptor provides a growth signal that determines the magnitude and duration of T-cell responses. Limited proteolysis studies provide the first direct biochemical evidence that the external region of the IL-2 receptor consists of two independent domains. 125I-labeled IL-2 has been chemically crosslinked to the receptor and proteolytic cleavage of the crosslinked product indicates that IL-2 is selectively bound to the N-terminal domain of the receptor.

The MRC OX-44 antigen marks a functionally relevant subset among rat thymocytes

A monoclonal antibody called MRC OX-44 is described that labels all myeloid cells and peripheral lymphoid cells but only 12% of thymocytes. The OX-44+ thymic cells include most if not all cells found in the medulla but only a small fraction of the cortical cells. Together with CD4 and CD8 antigens, seven subsets of thymic cell were defined and it was notable that most CD4- CD8- cells were OX-44+ whereas almost all CD4+ CD8+ cells were OX-44-. In functional tests, the OX-44+ cells accounted for all proliferation by thymocytes when stimulated by allogeneic spleen cells or concanavalin A plus growth factors and OX-44- cells were completely negative in these assays. Also, in tests for thymopoiesis after intra-thymic injection of cells, all activity was OX-44+. It seems possible that the OX-44+ set may include all functionally relevant cells in the rat thymus.

A canine lymphocyte surface antigen detectable by a monoclonal antibody (DT200)

A murine monoclonal antibody (DT200) was raised against a 210,000-dalton (210 K) lymphocyte surface protein (a member of the lymphocyte antigen known as T200) which was purified from a canine lymphoid tumor by preparative slab gel electrophoresis. In immunoblotting studies of electrophoretically separated plasma membranes from five cases of canine lymphoma, the antibody detected two antigenically intact peptides at 95 and 110 K which, based on previous polyclonal anti-210 K antiserum immunoblotting and peptide mapping studies, may represent the protease-resistant fragment of the canine T200 molecule. Since DT200 retains its reactivity in formalin-fixed, paraffin-embedded tissue sections, 13 dogs with malignant lymphoma and a panel of normal lymphoid and nonlymphoid tissues were studied using an indirect immunoperoxidase technique. The antigen was localized predominantly to the surface membrane of lymphoid cells. DT200 reacted strongly with all five histological subtypes of lymphoma tested while moderate reactivity was detected in normal B and T cell areas of lymph node, spleen and tonsil. Thymocytes and selected hemopoietic precursors were weakly reactive with DT200 while plasma cells, mature granulocytes, red cells and megakaryocytes were unstained. It was concluded that DT200 is a useful reagent for the diagnosis of malignant lymphoma particularly in extranodal sites and may prove valuable in the investigation of the structure and function of T200 in the dog.

MB1, a quail leukocyte-endothelium antigen: partial characterization of the cell surface and secreted forms in cultured endothelial cells

We describe here conditions allowing the selective growth in culture of embryonic capillary endothelial cells from quail yolk sac. Such cultures were set up to characterize an antigen present on the endothelial cell surface and to study whether it was secreted in the culture medium. This antigen, MB1, was previously evidenced by a monoclonal antibody raised to quail IgM heavy chain. It is present at the surface of all endothelial and hemopoietic cells (except mature erythrocytes) starting from the hemangioblast, the early mesodermal precursor of blood and vascular endothelial cells. The MB1 epitope is also found on quail plasma molecules of 80 and 125-200 kDa. By immunoprecipitation of either surface or metabolically labeled endothelial cellular material, we have chemically characterized MB1-bearing components as glycoproteins of apparent molecular mass ranging from 80 to 200 kDa and provided evidence for their release into the culture medium. This is consistent with the hypothesis that, in the quail, vascular endothelium participates in the secretion of the alpha-MB1-positive plasmatic components.

Surface Ly-5 glycoprotein in murine natural killer (NK) cell development, target binding and cytotoxicity

The role of surface Ly-5 glycoprotein expression in the binding and lysis of susceptible tumor targets by natural killer cells was studied using NK cell-enriched splenocytes from 6-8 week old C57BL/6 mice which were reacted with anti-Ly-5 serum in the presence or absence of a source of complement. A conjugate assay was used to demonstrate that abrogation of tumor cell lysis by anti-Ly-5 serum involved the inhibition of NK cell binding to susceptible YAC-1 targets. Additionally, reconstituted membrane vesicles from NK cell-enriched splenocyte populations blocked binding of effector cells to YAC-1 lymphoma targets, a phenomenon which was abrogated by pretreatment of vesicles with anti-Ly-5 serum. Indirect immunofluorescent labeling and cell sorting were used in the physical separation of Ly-5+ and Ly-5- cells to examine the effect of interferon and interleukin preparations on Ly-5 expression and Nk activity. Three hour treatment of sorted Ly-5- cells with murine alpha + beta interferon resulted in conversion of 22% of the cells to an Ly-5+ phenotype, as well as a significant increase in the percent specific lysis of NK-susceptible YAC-1 targets when compared to freshly sorted Ly-5- cells (29.5 +/- 1.9 vs 2.6 +/- 4.0; p less than .001). In vitro proliferation of sorted Ly-5- cells was induced by three week culture in an interferon- and interleukin-containing supernatant from ConA stimulated BALB/c splenocytes (CM), followed by repeat analysis of Ly-5 expression and cytotoxic activity. Cell sorter purified Ly-5- cells cultured in CM acquired substantial surface Ly-5 with concomitant high levels of cytotoxic activity that remained partially susceptible to inhibition by anti-Ly-5 serum. The data presented suggest that surface Ly-5 glycoprotein expression is important for binding of freshly isolated NK cells to YAC-1 targets. In addition, Ly-5- precursors of NK cells are present in murine splenic tissues and can be induced by CM to become highly active effector cells with increased surface Ly-5 expression. The persistent susceptibility of a subset of these cells to inhibition of cytotoxic activity by anti-Ly-5 serum provides additional evidence of an important role for the Ly-5 glycoprotein in the natural killer cell cytolytic mechanism against certain targets.

NK-9, a distinct sialylated antigen of the T200 family

The nature and properties of antigens detected by a novel monoclonal antibody, NK-9, were studied. The NK-9 antigens had apparent molecular masses of 190, 200 and 220 kDa and were sensitive to neuraminidase and sodium metaperiodate treatments, which destroy the sialic acid residues of the cell surface glycoproteins. Trypsin treatment also removed the NK-9 reactivity, but the antigens were restored within a few hours thereafter. Tunicamycin, which inhibits the N-linked glycosylation after neuraminidase treatment, had no effect on the reappearance of the NK-9 positivity. Neither did endoglycosidase F, which removes the N-linked sugars, abolish the NK-9 antigenicity. Monensin, which blocks the cellular secretion, inhibited the restoration of the antigens, and monensin block also without preceding treatment with neuraminidase led to the disappearance of NK-9 reactivity, suggesting possible recycling molecules as carriers of the NK-9 detected epitopes. The NK-9 antigens appear to belong to the T200 antigen family, but are distinct from the antigens reactive with the available anti-T200 antibodies anti-LC, T29/33 and HLe-1, based on their different cell type distribution and absence of cross-reactivity in sequential immunoprecipitations.

Identification and characterization of the human Pgp-1 glycoprotein

Two monoclonal antibodies have been raised against human Pgp-1 by the immunization of mice with human fibroblasts. The human molecule, like the previously identified mouse counterpart, is an abundant membrane protein (Mr approximately 95 000) with a broad tissue distribution. Pgp-1 is phosphorylated, and phosphoamino acid analysis demonstrates that this occurs exclusively on serine residues. A major difference between the mouse and the human is that 50-60% of human thymocytes are Pgp-1+ compared to 5-10% of mouse thymocytes at an equivalent stage in development. Immunofluorescence studies of cryostat sections showed that the majority of human medullary thymocytes are strongly stained with Pgp-1-specific antibody, whereas the expression of Pgp-1 on cortical thymocytes is much more heterogeneous.

MRC OX-52: a rat T-cell antigen

A mouse monoclonal antibody MRC OX-52 has been shown to label rat T lymphocytes and thymocytes. The molecule precipitated by this antibody from both thymocytes and T lymphocytes had a two-chain structure of 120,000 MW and 95,000 MW.

MRC OX-43: a monoclonal antibody which reacts with all vascular endothelium in the rat except that of brain capillaries

A mouse monoclonal antibody, MRC OX-43, has been shown to label vascular endothelium in all tissues of the rat except that of brain capillaries. Using immunoperoxidase staining, the antigen was shown to be expressed on the luminal surface of blood vessels. In addition, this antibody recognized a surface antigen on circulating erythrocytes and some macrophage populations, namely all those in the peritoneal cavity and a subset of alveolar macrophages. The antigen recognized by this antibody was identified on macrophages by metabolic and cell surface labelling followed by immunoprecipitation and sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) and found to be a surface protein of 90,000 MW.

Acquisition of cytotoxic T lymphocyte-specific carbohydrate differentiation antigens

Cytotoxic T cell (CTL)-specific activation antigens, termed CT determinants, have been detected by monoclonal antibodies (mAb) that inhibit CTL function. At the cell surface, the CT antigens are associated with the T200 glycoproteins and two other proteins of Mr 140,000 and 85,000 and are present on a secreted protein, gp155. Periodate treatment followed by binding analysis and immunoprecipitation experiments using tunicamycin-treated cells indicated that carbohydrate is necessary for CT antigen expression. Furthermore, gp155 is secreted in the presence of tunicamycin while retaining the CT antigens, and the CT determinants are added late in T200 biosynthesis, suggesting that the CT glycans are O-linked. Finally, interleukin 2 was shown to dramatically influence the expression of the CT mAb-reactive oligosaccharides present at the CTL cell surface.

Expression of murine Lm-1 locus. Lm-1 determinants on lymphocytes and macrophages, and effects of Lm-1 incompatibility on bone marrow grafts

Lm-1 is an Igh-linked locus that codes for cell surface alloantigens (Lm-1 determinants) recognized by T lymphocytes. Using Lm-1 congenic strains and cold-target inhibition of anti-Lm-1-specific lysis by cytotoxic T lymphocytes, we were able to demonstrate differential expression of two distinct Lm-1 antigenic determinants. One determinant is expressed on the surface of T cell blasts, the other on a number of pre-B cell lines. Both determinants are present on B cell blasts. Macrophages also bear Lm-1 determinants, and possibly express a determinant not found on lymphocytes. Fibroblasts, (unstimulated) thymocytes, and immature T cells lack detectable Lm-1 determinants. These data indicate that expression of the Lm-1 locus is dependent on cell lineage and the stage of cell differentiation or activation. We propose that Lm-1 is a lymphocyte-macrophage differentiation locus containing a number of structurally and functionally related genes. Evidence was presented that Lm-1 may also serve as a histocompatibility locus of major importance for bone marrow transplantation. Specifically, when Lm-1-incompatible bone marrow cells and spleen cells (from normal or anti-Lm-1 immune mice) were transplanted into X-irradiated recipients, the maturation and/or function of bone marrow-derived donor B cells was delayed or inhibited.

Analysis of lymphopoietic stem cells with a monoclonal antibody to the rat transferrin receptor

A mouse monoclonal IgG2a antibody, designated MRC OX-26, is shown to be specific for the rat transferrin receptor, but does not block transferrin binding. The antibody labelled a myeloma, three leukaemia cell lines and normal dividing cells of various types, but also bound to a number of nondividing normal tissues. No labelling of lymphopoietic stem cells could be detected, even though approximately 25% of bone marrow and over 95% of fetal liver cells were clearly labelled.

Identification of shared antigenic determinants of the putative human T lymphocyte antigen receptor

A mouse antiserum, anti-gp40,49 was obtained by immunizing BALB/c mice with the putative T cell antigen receptor isolated from HPB-MLT cells. This antiserum reacted with peripheral blood lymphocyte (PBL) and a panel of immunocompetent T cell lines and clones in each case precipitating from lysates of cells labeled by surface iodination, a disulfide-linked dimer consisting of an alpha subunit Mr (46,000-49,000) and a beta subunit Mr (40,000-45,000). Variability in Mr of the two subunits, particularly of the beta (light) subunit, was observed when the receptors of immunocompetent T cell lines with different antigen specificities were compared. Anti-gp40,49 serum reacted selectively with the alpha subunit after reduction and alkylation of the protein complex. These results confirm the relationship between the gp40,49 protein complex of HPB-MLT cells and the putative T cell antigen receptor on normal immunocompetent T cells and indicate that the alpha subunit of the human receptor expressed shared determinant(s) that are immunogenic in the mouse. Some features of the T cell antigen receptor appear to be unusual in that even with a xenoantiserum against the purified molecule, only antibodies against clonotypic determinants could be detected at the cell surface by quantitative immunofluorescence analysis.

Partial characterization of a transformation-specific glycopeptide in SSV-NP cells

An autologous antiserum against simian sarcoma virus-infected nonproducer cells (SSV-NP cells) recognized a SSV transformation-specific glycopeptide (SSV-TrSgp) [H.-J. Thiel, T.J. Matthews, E.M. Broughton, A.M. Butchko, and D.P. Bolognesi (1981) Virology 112, 642-650]. Gel filtration of this component on a Sephacryl S-200 column indicated an apparent molecular weight at about 200,000 (d). This antigen represented a proteoglycan-like molecule, as evidenced by the size of glycopeptides after Pronase treatment and by incubation with chondroitinases. The antigenicity of the SSV-TrSgp was completely destroyed after exposure to different proteases. On the other hand, incubation with neuraminidase or chondroitinases degraded the molecule to some extent, but did not affect its antigenicity as measured by immunoprecipitation. Trypsin and EDTA treatment of intact pulse-labeled cells, as well as surface iodination, indicated that the SSV-TrSgp represents a cell membrane-associated molecule.

Rabbit leukocyte surface antigens defined by monoclonal antibodies

Several monoclonal antibodies (mAb) against rabbit leukocytes were characterized in binding and functional studies. mAb 1.24 stains thymocytes, bone marrow cells, peripheral T and B cells and blood monocytes. T cells express more 1.24 antigen than B cells. In the absence of added complement (C), mAb 1.24 inhibits alloantigen-, concanavalin A (Con A)-, and phytohemagglutinin (PHA)-, but not pokeweed mitogen (PWM)- or anti-immunoglobulin (Ig)-induced cell proliferation. It also strongly blocks anti-sheep erythrocyte plaque-forming cell responses. A second mAb, designated 4.B9, binds to 20% of thymocytes and to most, if not all, peripheral T cells and in vitro-activated T cell blasts. A third one, 10.B3, is reactive with the nearly entire thymocyte and a major peripheral T cell population. Two-color membrane immunofluorescence reveals the presence of a small population of peripheral blood leukocytes which bear surface Ig and are weakly stained by mAb 4.B9 and 10.B3. Without C, both 4.B9 and 10.B3 inhibit Con A- and PHA-induced mitogenesis, but have no effect on PWM-, antigen-, or alloantigen-induced cell proliferation. Depletion of 4.B9+ cells by panning or complement lysis completely abrogates proliferative responsiveness to antigen and alloantigen, significantly reduces responsiveness to the T cell mitogens Con A and PHA, but enhances that to the B cell mitogen anti-Ig. A fourth mAb, 12.C7, binds to 60% of thymocytes and to 10-30% of peripheral T lymphocytes at high-level fluorescence. T cell blasts obtained in mixed leukocyte reactions are partially stained by mAb 12.C7, while those obtained after Con A or PHA activation are not. In addition, mAb 12.C7 is completely unreactive with B cells or monocytes. Without complement, it does not seem to interfere with any of the in vitro functions tested. All antigens studied here do not appear to be expressed in nonleukon tissues, as they do not bind to erythrocytes and are absent from brain, heart, liver and kidney as shown by quantitative absorption analysis.