Detection and characterization of lymphocytes bearing receptors for peanut agglutinin by a specific rosetting technique

Murine lymphocytes bearing receptors for peanut agglutinin (PNA) have been visualized using a specific rosetting technique. The lymphocytes were incubated with PNA and mixed with neuraminidase-treated sheep red blood cells. The percentage of the PNA rosetting lymphocytes found in the various organs studied was dependent upon the PNA concentration. In the spleen, the PNA rosetting lymphocytes were primarily T cells with low PNA concentration while both T and B lymphocytes were rosetted with high PNA concentration. In the fetal liver and thymus PNA rosetting lymphocytes were present in small amounts early in fetal life, increasing and reaching adult levels by late fetal life. The present study shows that the rosetting technique is more sensitive than previously described techniques for the detection of various lymphocyte subpopulation having receptors for PNA.     

Different T cell antigens and receptors for peanut agglutinin and Helix pomatia agglutinin on steroid-sensitive and resistant lymphocytes in the rabbit using double immunofluorescence

Rabbit T lymphocytes were characterized using fluorochrome-labelled antisera against thymus cell determinants and fluorochrome-labelled lectins. Three anti-T cell antisera were used, detecting different antigenic determinants on the majority of T cells. Only small subpopulations were found stained by one of the three antisera. After dexamethasone (DX) treatment, the proportion of T cells was significantly increased in bone marrow and appendix, presumably by different mechanisms. Cells binding peanut agglutinin, mainly belonging to the T cell population, were present in small numbers in thymus, spleen, lymph node, and appendix from normal as well as from DX-treated animals. In bone marrow, however, a large PNA+ population showing neither T nor B cell surface properties was observed. After treatment with neuraminidase (NA), PNA binding sites were exposed on B as well as on an increased number of T cells. It is suggested, therefore, that T and B cells retained their PNA receptors during maturation. Masking of these receptors will take place before differentiation of T cells is initiated within the thymus. After NA treatment, also binding sites for Helix pomatia agglutinin were exposed on T cells and to different extents, revealing subsets of negative, weakly and strongly positive HPA cells. HPA weakly positive cells form the major population present in the thymus, while HPA strongly positive cells constitute the major population of the T cells in spleen and lymph node. The exposure of receptors for PNA of HPA appears not to be related to the steroid sensitivity of the cells.     

Peanut agglutinin. II. Characterization of the Thy-1, Tla and Ig phenotype of peanut agglutinin-positive cells in adult, embryonic and nude mice using double immunofluorescence.

The Thy-1, Tla and Ig phenotype of peanut agglutinin (PNA)-binding cells was characterized in various strains of mice. In the thymus, PNA was found to bind principally but not exclusively to the Thy-1+ Tla + Ig-- steroid-sensitive cortical thymocytes. Thy1 + Tla -- Ig -- steroid-resistant cells are not labeled with PNA. In other lymphoid organs, PNA bound to a minority of T or null cells but generally not to B cells. During ontogeny, PNA + and PNA -- T lineage cells appear simultaneously in the liver at day 10 of gestation, in the thymus at day 11 and in the spleen at day 18. No evidence was found for a maturation from PNA + to PNA -- cells. Prethymocytes present in nude mice were also divided into a PNA + and PNA -- population.     

Peanut agglutinin (PNA)-binding properties of murine thymocyte subpopulation.

Surface receptors for peanut agglutinin (PNA), a lectin with D-galactose specificity, were detected on mouse thymocytes using fluorescence microscopy. Depending on mouse strain, 69-85% of unseparated thymocytes could thus be characterized as PNA+. Electrophoretic fractionation of thymocytes from normal or immunosuppressive drug-treated donors revealed an inverse relationship between PNA-binding properties and cell electrophoretic mobility (EPM). Thus, all thymocytes recovered in the lowest EPM fractions were strongly PNA+ whereas those in the highest EPM fractions were in the majority PNA-. Most of the cells collected in the intermediate EPM range were PNA+ but staining with the fluoresceinated lectin appeared weaker than for the low EPM thymocytes. Reciprocal experiments in which thymocytes were separated by PNA-mediated aggregation into fractions with different affinities for the lectin and then subjected to physical analysis, definitely established that PNA+ cells are of lower EPM than PNA- cells and that these two cell types also differ in size distribution. These data show that the four physical subpopulations of thymocytes previously described present distinctive PNA-binding properties: Th1 and Th2 cells can be classified as strongly PNA+, Th3 cells as less intensely PNA+, and Th4 cells as mostly PNA-.     

Lectin-binding patterns of small lymphocytes in bone marrow,thymus and spleen: demonstration of lymphocyte subsets by quantitative radioautography

Cells from mouse bone marrow, thymus and spleen were exposed to ¹²⁵I-labeled concanavalin A (Con A), Lens culinaris lectin (LCL), soybean agglutinin (SBA), Helix pomatia agglutinin (HPA), phytohemagglutinin-P (PHA-P), peanut agglutinin (PNA), or wheat germ agglutinin (WGA) in a range of concentrations and examined radioautographically. Small lymphocytes in the three organs differed in the minimal concentration of each lectin which gave detectable surface labeling, while at optimal lectin concentrations, their labeling intensity profiles differed markedly. Inhibition by sugars demonstrated the labeling specificity. Major populations of bone marrow small lymphocytes bound WGA strongly, while Con A, SBA, HPA, PHA-P and LCL were bound only weakly, and PNA binding was lacking. Most thymus cells bound Con A, SBA, HPA, PHA-P and PNA strongly, WGA and LCL weakly. Subsets of bone marrow and thymus small lymphocytes differed from the major populations in their lectin-binding intensities. Spleen small lymphocytes were heterogeneous in the binding of each lectin. However, a major population bound LCL exceptionally strongly, while few cells bound PNA. Using a panel of lectins under standardized conditions, these studies show distinctive lectin-binding patterns for small lymphocytes in the bone marrow, thymus and spleen, respectively. Major and minor cell populations are distinguishable in each organ, providing an approach to discriminating lymphocyte lineages, subtypes and differentiation stages.     

The requirement for tetravalency of soybean agglutinin for induction of mitogenic stimulation of lymphocytes.

The mitogenic activity of soybean agglutinin was found to depend on the presence of lectin aggregates formed in lectin preparations stored in the lyophilized state. Such soybean agglutinin preparations gave maximal stimulation of untreated pig lymph node cells and neuraminidase-treated mouse spleen cells at relatively high concentrations, ranging from 100 to 2000 mug/ml. After separation into unaggregated (divalent) and polymeric (tetra-and multivalent) fractions, it was found that the unaggregated lectin did not stimulate the cells, while the tetravalent and multivalent fractions were active and gave maximal stimulation at a concentration of 10 mug/ml. These results suggest that soybean agglutinin must have at least four sugar binding sites in order to be able to stimulate lymphocytes.     

Influence of protein restriction on lymphoid cell populations characterized by the binding of peanut agglutinin

Cells binding peanut agglutinin (PNA) were studied in the thymus, spleen, and mesenteric lymph nodes from mice placed in the post weaning period on protein-restricted diets containing 8% (R8%) and 4% (R4%) casein. The proportion of PNA+ thymocytes and the absolute number of total and PNA+ cells in the thymus were significantly diminished in R8% and R4% mice. Larger proportion of PNA+ thymocytes showed weaker fluorescence in R8% and R4% than in normally fed (N) animals. Recovery of PNA+ thymocytes was observed in R8% but not in R4% mice at 8 weeks. The number of total and PNA+ cells was significantly diminished although the proportion of PNA+ cells was not modified in the peripheral lymphoid organs of R8% and R4% mice. Results indicate that protein restriction preferentially affected the immature cortical PNA+ cells in the thymus whereas cell depletion in the peripheral lymphoid organs occurred at the expense of both the PNA+ and PNA- subpopulations.     

The selective expression of distinct fucosylated glycoproteins on murine T and B lymphocyte subsets

The putative expression of distinct terminally fucosylated glycoconjugates among murine lymphocyte subpopulations was sought using Ulex europaeus agglutinin-I (UEA-I) and Anguilla anguilla agglutinin (AAA), each with a distinctive primary binding preference to type II and type I blood group H oligosaccharide determinants, respectively. In newly born and adult mice, direct labeling of isolated lymphocyte subsets in suspension, as well as immunohistochemical assays were indicative of the age-regulated co-expression of the UEA-I-reactive ligand among thymic epithelial cells and a subset of the mature (PNA-), medullary thymocytes. In the spleen, UEA-I-ligand expression was selectively confined to a subset of the CD4+ T lymphocytes scattered around red pulp sinuses in newly born mice, but distinctively localized within the T cell-dependent periarteriolar lymphoid sheath compartment in adult mice. Among thymocytes of adult mice, two-dimensional Western blots demonstrated the expression of the UEA-I-reactive ligand among multiple isoforms of three major 50, 114 and 180kDa acidic glycoproteins, of which, heterogeneous weight and charge variants of the 114kDa component were also evident among splenocytes. The expression of the AAA-reactive ligand was, on the other hand, restricted to a single major 120 kDa acidic glycoprotein, in addition to a minor molecular weight variant of 115kDa, associated with a subset of immature IgM+ B lymphocytes localized within the red pulp, in both newly born and adult mice. The significance of these findings is discussed in relation to mechanisms that govern lymphocyte maturation, selection and migration.     

A 160-kilodalton epithelial cell surface glycoprotein recognized by plant lectins that inhibit the adherence of Actinomyces naeslundii.

The adherence of Actinomyces naeslundii to human epithelial (KB) cells is mediated by the interaction of a fimbrial lectin on this oral bacterium with epithelial cell receptors exposed by sialidase. The D-galactose- and N-acetyl-D-galactosamine-reactive plant lectins from peanut and from Bauhinia purpurea inhibit this interaction. This report describes the partial purification and characterization of a 160-kilodalton (kDa) cell surface glycoprotein which is the principal receptor for these lectins. Radioiodinated lectins detected a band of 160 kDa on sialidase-treated Western blots of epithelial cell extracts but did not detect bands on nontreated filters. However, wheat germ agglutinin was reactive with the 160-kDa band on filters that were not treated with sialidase, suggesting that this lectin recognizes the sialic acid residues of this molecule. The 160-kDa component was partially purified from n-octylglucoside extracts of the epithelial cells by wheat germ agglutinin affinity chromatography. This molecule was metabolically labeled with D-[14C]glucosamine and labeled at the cell surface by lactoperoxidase-catalyzed iodination or periodate oxidation followed by sodium borotritide reduction. Incubation of epithelial cells with sialidase before extraction resulted in the loss of the 160-kDa band and the appearance of a band at 200 kDa which was directly reactive with 125I-labeled peanut agglutinin. These results indicate that the 160-kDa glycoprotein on the surface of the epithelial cell serves as a receptor for the agglutinins from the peanut and B. purpurea and presumably the fimbrial lectin of actinomyces.     

The 70-kilodalton pertussis toxin-binding protein in Jurkat cells.

125I-ASD photoaffinity-labeling derivatives of pertussis toxin (125I-ASD-PT) or lipopolysaccharide (125I-ASD-LPS) labeled similar 70-kDa proteins in Jurkat cells, a cell line derived from human CD4+ T lymphocytes. Labeling of this 70-kDa protein by 125I-ASD-PT was inhibited by underivatized PT but not by underivatized LPS. However, an immunoglobulin M monoclonal antibody with specificity for the p73 LPS receptor in murine splenocytes (S. W. Bright, T.-Y. Chen, L. M. Flebbe, M.-G. Lei, and D. C. Morrison, J. Immunol. 145:1-7, 1990) inhibited 125I-ASD-PT labeling of the 70-kDa species in Jurkat cells. Our results suggested that PT may bind to the same 70-kDa protein as LPS does in Jurkat cells but that PT and LPS bind to different sites on this receptor candidate. 125I-ASD-PT photoaffinity labeling of the 70-kDa protein was also inhibited by underivatized glycoproteins to which PT has been shown to bind, and this inhibition correlated with the relative binding affinities of the glycoproteins for PT. 125I-ASD derivatives of two sialic acid-specific plant lectins, Maackia amurensis leukoagglutinin and Sambucus nigra agglutinin, with oligosaccharide binding specificities similar to those of PT also labeled a 70-kDa protein in Jurkat cells. This suggests that the 70-kDa PT receptor candidate in Jurkat cells likely contains sialooligosaccharide sequences to which PT, M. amurensis leukoagglutinin, and S. nigra agglutinin bind. The cross-reacting epitope recognized by monoclonal antibody 5D3 in this 70-kDa species might overlap the PT- and LPS-binding sites.     

PNA Lectin-Based Separation of Thymocytes into Mature and Immature Subpopulations: CD4-8- Double Negative Cells Display Characteristics of PNAlo Mature Thymocytes

Cortical (immature) thymocytes are widely reported to express intermediate to high levels of receptors for the lectin, peanut agglutinin (PNA). Light-scatter studies of murine fetal thymocytes stained with PNA or anti-mouse CD4 and CD8 monoclonal antibodies indicated, however, that the most immature CD4-8- (DN) thymocyte subpopulation binds levels of PNA commonly described as PNA^lo. Evaluation of the PNA binding characteristics of fetal thymocytes negative for the CD8 antigen confirmed the existence of a major population (approximately 20% of total cells) of CD4^-8^- PNA^lo fetal thymocytes. The majority of these DN thymocytes were subsequently found to bind sub-agglutinating levels of PNA, similar to mature CD4⁺ or CD8⁺ single positive (SP) thymocytes. Given this information, an immunomodulating compound (2,3,7,8-tetrachlorodibenzo-p-dioxin; TCDD) known to produce a maturational delay in murine thymocytes was tested for a possible concurrent effect on thymocyte PNA lectin binding. A TCDD- induced increase in DN thymocytes was found to be paralleled by an increase of equal magnitude in PNA^lo thymocytes. Taken together, these data provide evidence that acquisition of the PNA receptor may be a maturational event occurring during the DN stage of thymocyte ontogeny. Further, these results suggest that separation of thymocytes into mature (medullary) and immature (cortical) subpopulations by PNA agglutination may result in contamination of medullary cells by the most immature (DN) subpopulation of thymocytes.     

Expression of binding sites for peanut agglutinin during murine B lymphocyte differentiation.

Haemopoietic cells from several murine organs were examined for the presence of peanut agglutinin (PNA) receptors. Foetal liver and adult bone marrow contained a number of cells, which were PNA+ but did not stain with conventional T and B markers. Some of the PNA+ cells, however, were pre-B cells, as shown by the presence of cytoplasmic IgM in the absence of cell surface Ig. Cells in the T lineage retained their PNA receptors during maturation, although these became masked by sialic acid on mature peripheral blood T cells. Cells of the B lineage, in contrast, gradually lost their PNA receptors as they matured from pre-B to mature surface immunoglobulin positive B lymphocytes.     

Proline-rich polypeptide (PRP) from ovine colostrum. Bi-directional modulation of binding of peanut agglutinin, resistance to hydrocortisone, and helper activity in murine thymocytes

A proline-rich polypeptide (PRP) isolated from ovine colostrum has a regulatory effect on the immune response. The present report demonstrates that the polypeptide can cause bi-directional modulation of surface markers and function of murine thymocytes. PRP is able to reduce binding of peanut agglutinin (PNA) to murine PNA+ thymocytes and to increase the binding of PNA to PNA- cells. This transition of binding ability can be reversed by a second treatment of cells with PRP. PRP is also able to transform cortisone-resistant thymocytes into cortisone-sensitive, and vice versa. Helper cells induced by PRP from murine glass-nonadherent thymocytes (PNA+) showed suppressor activity after the second treatment with PRP. The observed changes were occurring concomitantly, i.e. changes in binding of PNA were accompanied by changes in resistance to cortisone and in expression of helper or suppressor activity. Bi-directional effects of PRP on PNA-binding ability, sensitivity to hydrocortisone, and helper-suppressor function, makes this polypeptide unique among immuno-modulators known.     

Duck lymphocytes. I. Purification and preliminary observations on surface markers

High yields of lymphocytes were obtained by centrifuging duck blood, collected into an equal volume of heparinized phosphate-buffered saline, over Ficoll-diatrizoate, sg. 1.077, for 25 min at 200 X g. These lymphocytes did not form E rosettes under a variety of conditions, or EA rosettes with sheep erythrocytes sensitized with rabbit antibodies. High proportions (50-80%) of blood and organ (thymus, bursa of Fabricius, spleen, cervical lymph node) lymphocytes had surface immunoglobulin (SmIg). The proportion of blood lymphocytes with SmIg was reduced (to 16-73%) by previous incubation in serum-free medium; less reduction occurred after similar incubation of organ lymphocytes. With or without previous treatment with neuraminidase duck lymphocytes did not express receptors for Helix pomatia lectin. However, some untreated lymphocytes did have receptors for peanut agglutinin (PNA) and the number was increased after desialation. The proportions and organ distribution of lymphocytes with SmIg or receptors for PNA did not follow a pattern consistent with any expected distribution of T and B cells. Duck blood lymphocytes were separated into 2 bands (mean densities 1.026 and 1.068 g/cm3) in Percoll gradients. These did not differ in expression of SmIg and receptors for PNA, but only the upper band (sg. 1.026) responded to phytohaemagglutinin, concanavalin A, pokeweed mitogen and rabbit anti-duck immunoglobulin serum in lymphocyte transformation tests. Blood lymphocytes were also separated according to their adherence to nylon wool. There was no difference in surface markers between the adherent and non-adherent cells, but only the adherent population responded to mitogens. It is suggested that since ducks are phylogenetically close to the amphibians and reptiles their lymphocyte populations may not express surface markers similar to those of chickens and mammals.     

The predominant heavily glycosylated glycoproteins at the surface of rat lymphoid cells are differentiation antigens.

Rat lymphoid cells have been labeled with sodium 3H-borohydride after periodate oxidation. The labeled glycoproteins were solubilized in detergent and analyzed by fluorography after polyacrylamide gel electrophoresis in sodium dodecyl sulfate. Major bands were found at 150 000, 95 000 and 25 000 apparent mol.wt. for thymocytes; at 170 000 and 95 000 mol. wt. for T lymphocytes and at 200 000 mol.wt. for B lymphocytes. Bone marrow cells showed a diffuse band at 100 000 mol.wt. with relatively minor bands around 150 000 mol.wt. With the exception of the 95 000 mol. wt. bands, all these glycoproteins bound to lentil lectin. Using monoclonal or monospecific antibodies in immunoprecipitation and on antibody affinity columns, each of these glycoprotein bands was identified as a previously defined lymphocyte differentiation antigen. The bands at 150 000 mol.wt. on thymocytes, at 170 000 on T lymphocytes, at 200 000 on B lymphocytes, and at 130 000 to 150 000 on bone marrow cells all consist of a leukocyte-common antigen, which has previously been shown to be present on leukocytes but not on other tissues. At least a part of the 95 000 mol.wt. band on thymocytes, T lymphocytes and bone marrow cells is the W3/13 antigen previously shown to be on mature T lymphocytes, polymorphonuclear cells, and in brain. The 25 000 mol.wt. band of thymocytes is the Thy-1 antigen. Similar experiments were carried out on thymocytes labeled with ¹²⁵I by the lactoperoxidase method. An intense band at 150 000 mol. wt. was identified as the leukocyte-common antigen by immunoprecipitation. A labeled band, which did not bind to lentil lectin, was immunoprecipitated at 95 000 mol. wt. with W3/13 antibody. Rat Thy-1 antigen was not labeled with ¹²⁵I.     

Lectin histochemistry of galactose and N-acetyl-galactosamine glycoconjugates in normal gastric mucosa and gastric cancer and the relationship with ABO and secretor status

The histochemical binding of four lectin-peroxidase conjugates to normal human gastric mucosa and gastric carcinoma is described. The lectins were peanut agglutinin (PNA) which is specific for galactose residues and soy bean agglutinin (SBA), Dolichos biflorus agglutinin (DBA) and Helix pomatia agglutinin (HPA) which are specific for N-acetylgalactosamine. Binding of PNA to surface mucous cells or normal gastric mucosa occurred in non-secretors but not secretors and was independent of ABO blood group at all sites. PNA binding was unrelated to the immunohistochemical demonstration of Thomsen-Friedenreich (T) antigen. DBA and HPA bound selectively to surface mucous cells in normal gastric mucosa from group A secretors but binding at other sites was independent of ABO status. SBA binding showed no relationship with blood group or secretor status. In gastric cancers the major finding was the occurrence of extensive masking of lectin binding sites by sialic acid which was not seen in normal mucosa. Sialic acid masking was most marked with PNA and least marked with DBA. There was no correlation between lectin binding patterns and the stage or differentiation of tumours. Results are consistent with in vitro studies demonstrating increased sialation of membrane glycoproteins following malignant transformation. Difficulties in interpreting the histochemical demonstration of lectin binding in terms of specific glycoconjugates are discussed.     

PNA Lectin-Based Separation of Thymocytes into Mature and Immature Subpopulations: CD4–8- Double Negative Cells Display Characteristics of PNAlo Mature Thymocytes

Cortical (immature) thymocytes are widely reported to express intermediate to high levels of receptors for the lectin, peanut agglutinin (PNA). Light-scatter studies of murine fetal thymocytes stained with PNA or anti-mouse CD4 and CD8 monoclonal antibodies indicated, however, that the most immature CD4–8- (DN) thymocyte subpopulation binds levels of PNA commonly described as PNA^lo. Evaluation of the PNA binding characteristics of fetal thymocytes negative for the CD8 antigen confirmed the existence of a major population (approximately 20% of total cells) of CD4^?8^? PNA^lo fetal thymocytes. The majority of these DN thymocytes were subsequently found to bind sub-agglutinating levels of PNA, similar to mature CD4⁺ or CD8⁺ single positive (SP) thymocytes. Given this information, an immunomodulating compound (2,3,7,8-tetrachlorodibenzo-p-dioxin; TCDD) known to produce a maturational delay in murine thymocytes was tested for a possible concurrent effect on thymocyte PNA lectin binding. A TCDD- induced increase in DN thymocytes was found to be paralleled by an increase of equal magnitude in PNA^lo thymocytes. Taken together, these data provide evidence that acquisition of the PNA receptor may be a maturational event occurring during the DN stage of thymocyte ontogeny. Further, these results suggest that separation of thymocytes into mature (medullary) and immature (cortical) subpopulations by PNA agglutination may result in contamination of medullary cells by the most immature (DN) subpopulation of thymocytes.     

Adenosine deaminase activity in lymphocyte subpopulations of B-16 melanoma and normal C57BL bearing mice

The activity of adenosine deaminase (ADA) was measured in thymus and spleen subpopulations separated by peanut agglutinin (PNA) of melanoma B-16 C57BL bearing mice and normal age-matched C57BL mice. Groups of 10 mice were used each time and the experiments were repeated 6 times. The adenosine deaminase activity in the PNA+ thymocytes of B-16 bearing mice was about 2.5 times lower than that of the normal C57BL mice while the ADA activity in the PNA+ fraction of spleen of the B-16 melanoma bearing mice was 2.5 times higher. These results demonstrate that the tumor burden probably induces a different redistribution and traffic of lymphocytes from one lymphopoietic organ to another. This traffic can also explain the thymus involution and spleen enlargement found in the B-16 mice.     

Separation of mouse T cell subsets by a fluorescent activated cell sorter using fluorescence-labeled peanut agglutinin.

Nylon non-adherent spleen T cells obtained from concanavalin A-injected mice were labeled with fluorescein-labeled peanut agglutinin and separated into peanut agglutinin-positive (PNA+) cells and peanut agglutinin-negative (PNA-) cells by a fluorescent activated cell sorter. PNA+ cells were found to exert marked suppressive effect on primary anti-sheep red blood cells antibody response, but PNA- cells did not affect the antibody response. From these results and from the sugar-binding specificity of PNA, suppressor T cells are supposed to possess abundant galactosyl residues exposed on the cell surface, which are not masked by sialyl residues.     

Cellular immunology in the baboon (Papio cynocephalus): examination of structural and functional characteristics of adult and fetal lymphoid cells

We studied structural and functional characteristics of lymphocytes from adult and fetal baboons (Papio cynocephalus). Flow cytometry with monoclonal antibodies to human lymphocyte antigens and plant lectins was used to define expression of surface antigens on lymphocytes from adult and 140 day fetal baboons (term = 180 days). Major T cell antigenic determinants on adult and fetal baboon lymphocytes were the Tp50, Tp32-45, and p45 glycoproteins detected by monoclonal reagents T11, OKT8, and OKT10 respectively. Baboon T lymphocytes did not react with the OKT3/anti-Leu4 or OKT4/anti-Leu3a reagents which detect, respectively, Tp19-29 and Tp55, major surface glycoproteins on human T lymphocytes. OKT6, which identifies the human TL antigen equivalent on thymocytes, did not react with baboon thymocytes. These data demonstrate major evolutionary divergence between human and baboon T lymphocytes. By contrast, baboon lymphocytes resembled human peripheral lymphocytes in reactivities with several non-T cell reagents. Lectin binding studies revealed substantially fewer peanut agglutinin-and wheat germ agglutinin-binding cells in suspensions of baboon fetal splenocytes and adult peripheral lymphocytes compared with fetal thymocytes. Therefore, maturation of baboon T lymphocytes is associated with loss of surface carbohydrate structures that bind these lectins. Adult and fetal baboon lymphocytes resembled human and murine lymphocytes in their capabilities to respond to mitogens and to produce interleukin-2. As in other species, adult, but not fetal baboon lymphocytes, mediated NK activity against a variety of nucleated target cells. Despite divergence in lymphocyte antigen expression, baboon lymphocyte functional development closely parallels that seen in humans.