Surface Immunoglobulin Positive Cells Research Articles

Recombinant Hsp33 and OmpC protein can serve as promising divalent vaccine with protection against Vibrio anguillarum and Edwardsiella tarda in flounder (Paralichthys olivaceus)

Vibrio anguillarum and Edwardsiella tarda are severe aquaculture pathogens shared similar epidemiological characteristics and susceptible to flounder (Paralichthys olivaceus). In our previous studies, recombinant(r) protein heat shock protein 33 (rHsp33) from V. anguillarum and outer membrane protein C (rOmpC) from E. tarda were proved to have protection against V. anguillarum and E. tarda, respectively. In this paper, the cross protection of rHsp33 against E. tarda and rOmpC against V. anguillarum, and the protection of divalent vaccine candidate (rHsp33 + rOmpC, rHC) against both V. anguillarum and E. tarda were evaluated. RHC, rHsp33, and rOmpC were vaccinated to flounder, respectively, and the percentages of surface immunoglobulin-positive (sIg+) cells in peripheral blood lymphocytes (PBLs), serum IgM, specific antibodies against V. anguillarum or E. tarda, specific antibodies against rHsp33, rOmpC or rHC, the expression of immune-related genes and relative percent survival (RPS) against V. anguillarum or E. tarda were measured. The results showed that: RHC could induced the enhancement of sIg + cells and high levels of specific antibodies against both V. anguillarm and E. tarda; Also a significant increase of specific antibodies against rHsp33, rOmpC or rHC, and up-regulation of gene expression of CD3, CD4-1, CD4-2, CD8α, CD8β and IgM in spleen, head-kidney, and hindgut, RPS of 70 ± 3.45% against V. anguillarum and 60 ± 1.48% against E. tarda, respectively. In addition, rHsp33 induced specific antibodies against E. tarda and rOmpC, and had a RPS of 43.3 ± 3.73% against E. tarda; rOmpC could evoke specific antibodies against V. anguillarum and rHsp33, and had a RPS of 44 ± 1.27% against V. anguillarm; The results demonstrated that there was cross protection of rHsp33 against E. tarda and rOmpC against V. anguillarum, rHC as a divalent vaccine can induce significant immune response and efficient protection against both E. tarda and V. anguillarum in flounder.

Monoclonal antibodies recognizing serum immunoglobulins and surface immunoglobulin-positive cells of Catla catla (Hamilton, 1822)

Monoclonal antibodies recognizing serum immunoglobulins and surface immunoglobulin-positive cells of Catla catla (Hamilton, 1822)

Distribution of immunoglobulin-positive cells in the spleen and kidney of Japanese flounder Paralichthys olivaceus

SUMMARY: The distribution of surface immunoglobulin-positive (sIg+) cells in the spleen, the head-kidney, and the trunk-kidney of adult Japanese flounder Paralichthys olivaceus was investigated by a flow cytometric analysis using a monoclonal antibody FB17 against flounder immunoglobulin M. Although the percentage of sIg+ cells varied among organs, a good correlation was revealed between the percentage in the head-kidney and that in the trunk-kidney (r = 0.996, P < 0.001). In contrast, no correlation was obtained between the percentage of sIg+ cells in the spleen and the head-kidney or trunk-kidney. The head-kidney and the trunk-kidney contained cells bearing fewer sIg that were stained dimly by FB17 in addition to brightly stained sIg+ cells regarded as mature B cells, while the spleen contained only sIg+ cells stained brightly. Moreover, the immunocytochemical analyses showed that the head-kidney contains plasma cells with strongly stained cytoplasm in addition to B cells with stained cell surface, which suggests that the cells with fewer sIg detected by flow cytometric analysis are presumed to be at a stage during the processes of differentiation to plasma cells. These results suggest that there are some differences between the spleen and kidney in the role of the immune system and it is considered that differentiation of B cells to plasma cells occurs in the kidney.

Differential cytochemical staining characteristics of channel catfish leukocytes identify cell populations in lymphoid organs

This is one of the first characterizations of channel catfish ( Ictalurus punctatus) leukocytes by enzyme cytochemistry. Leukocytes demonstrated cytoplasmic staining patterns very similar to mammalian leukocytes when stained with acid phosphatase, α-naphthyl butyrate esterase, β-glucuronidase, α-naphthyl acetate esterase, Sudan Black B and anti-immunoglobulin specific immunohistochemistry. Lymphocytes, monocytes, macrophages, neutrophils, and surface immunoglobulin positive (surface Ig+) cells were present in channel catfish renal hematopoietic tissue and spleen and demonstrated distinctive cytoplasmic foci staining patterns, cytoplasmic blushing or cell membrane staining. Monocytes, macrophages, lymphocytes and surface Ig+ cells were present in the thymus. Thymic and splenic cellular organization appeared very similar to these same mammalian tissues. In the thymus, acid phosphatase positive cells were distributed throughout the parenchyma, while α-naphthyl butyrate esterase and β-glucuronidase positive cells were concentrated in the cortex and the medulla, respectively. Surface immunoglobulin positive cells occurred in the cortex. In the spleen, acid phosphatase positive cells were scattered throughout the parenchyma, while α-naphthyl butyrate esterase positive cells were scattered throughout the parenchyma and adjacent to splenic arterioles. β-glucuronidase and surface immunoglobulin positive cells were restricted to immediately adjacent to splenic arterioles. Sudan Black B positive cells were scattered throughout the parenchyma, while α-naphthyl acetate esterase positive cells occurred adjacent to peri-arteriole lymphoid sheaths and appear very similar to mammalian metallophils.

Effect of tylosin tartrate on humoral immune responses in chickens.

While many antimicrobial agents have been reported to cause immunosuppression in animals, macrolide antibiotics enhance the immune function. Tylosin tartrate is a macrolide antibiotic approved for the control of mycoplasmosis in poultry. The purpose of this investigation was to determine the effect of tylosin on the humoral immune functions in chickens. Three days after oral tylosin tartrate administration, 4- or 8-week-old chickens were immunized intravenously with carbolic acid-killed Brucella abortus bacterin or sheep red blood cells. Seven days (plasma antibodies titre) or 4 days (antibody forming cells) post-immunization, there was a significant increase in antibody production as well as in the numbers of antibody-producing cells in tylosin tartrate-administered chickens compared with the untreated controls. However, 3 days after tylosin tartrate administration, there was no difference in the distribution of T-lymphocyte subpopulations (CD4 or CD8 positive cells) or B lymphocytes (surface immunoglobulin positive cells) in either the peripheral blood or spleens or untreated control chickens.

The cellular response of lambs to Brucella ovis before and after birth

The immunological response of lambs to Brucella ovis before and after birth was investigated. The establishment of indwelling cannulas in the efferent prescapular lymphatic ducts of foetal lambs allowed continual monitoring of the immune response of a single lymph node. Foetal lambs in the last trimester of pregnancy were shown to mount a strong cell-mediated immune response to B. ovis. Lymphocytes from the challenged lymph node stimulated with B. ovis in vitro usually first reacted significantly and had highest [ 3H]-thymidine incorporation between 4 and 6 days after primary and secondary challenge, whereas, lymphocytes from the unchallenged node did not exhibit significant [ 3H]-thymidine incorporation until some 24 h later. Lymphocytes from these lambs challenged as foetuses still exhibited significant [ 3H]-thymidine incorporation in response to B. ovis for 4 to 5 months after birth. The proportion of surface immunoglobulin-positive cells in efferent prescapular lymph of unchallenged lambs ranged from 0.5 to 2.0% but after B. ovis challenge this proportion ranged from 2.7 to 8.7% between 4 to 6 days after challenge. By 9 to 12 days after challenge, the proportion had declined to pre-challenge values.

A Tumor-Derived Serum Component Toxic to Surface Immunoglobulin-Positive Cells.

6B3 antigen, a serum component released by various human malignant cells, was examined for its effect on cultured cells, and a possibility was raised that it suppresses B cell function. The 6B3 antigen, purified from culture supernatants of a human lung cancer cell line, HLC-2, can bind to the surface of surface immunoglobulin (sIg)-positive cells in general and exerts cytostatic and cytocidal effects on them. On the other hand, it did not bind to sIg-negative cells. The binding was inhibited by soluble immunoglobulins only at high concentrations, suggesting that the antigen, which has a decameric subunit structure, has strong affinity for clustered sIg, whereas its affinity for monomeric immunoglobulins is relatively low.

Influence of flumequine on in vivo mitogen responses of European eel ( Anguilla anguilla L., 1758) lymphoid cells

The influence of flumequine on mitogen induced lymphoid cell proliferation in European eels ( Anguilla anguilla L., 1758) was studied. For this purpose an in vivo test, using peroral drug administration followed by successive intraperitoneal injections with concanavalin A (ConA) or bacterial lipopolysaccharides (LPS) and 5-bromo-2′-deoxyuridine, was applied. Direct counting of proliferated cells in blood smears revealed that flumequine possesses mitogenic properties. A synergistic and an antagonistic effect of the drug was observed after LPS and ConA stimulation, respectively. Flow cytometric analysis of peripheral blood lymphoid cells showed a significant reduction of the mean proportion surface immunoglobulin positive cells in the flumequine-treated animals. It is concluded that flumequine enhances proliferation of lymphoid cells (probably surface immunoglobulin negative cells) in eel under the present experimental conditions.

CD5-negative cell mediated experimental hypersensitivity pneumonitis.

Experimental hypersensitivity pneumonitis (EHP) can be transferred to Strain 2 guinea pigs by peripheral lymph node (PLN) cells cultured in vitro with antigen. The phenotype of the active cells has not been delineated. In addition, it is not known if cultured lung-associated lymph node (LALN) cells can transfer EHP. PLN and LALN cells from donor animals were cultured with a soluble extract of Micropolyspora faeni (10 micrograms/ml), and blast cells were isolated by centrifugation over Percoll gradients. Cultured PLN cells were passed through nylon wool columns, and the adherent and nonadherent fractions were tested for their ability to transfer EHP. PLN blast cell populations were depleted of CD5+ cells by treatment with monoclonal anti CD5 antibody (8BE6) and complement. Syngeneic recipients received media or LALN or PLN blast cells treated with antibody plus complement, media, or complement intravenously. Recipients were challenged intratracheally with M. faeni 48 h after the cell transfer, and they were killed 4 days later. The nonadherent PLN cell population was enriched for CD5+ (T) cells and depleted of surface immunoglobulin-positive (SIg+) cells. Treatment of the PLN blast cell population with 8BE6 and complement decreased CD5+ cells from 25 to 4% and increased SIg+ cells from 62 to 80%. All animals were maintained in HEPA-filtered air. Randomly selected microscopic fields of the lung (250/animal) were judged to be normal or abnormal without knowledge of treatment. There was a low level of pulmonary response to an intratracheal challenge of M. faeni in media recipients. There was a substantial increase (p less than 0.01) of the extent of pulmonary abnormalities in the animals receiving cultured PLN cells.(ABSTRACT TRUNCATED AT 250 WORDS)

The stromal cell line S17 supports the growth of lipopolysaccharide-stimulated CBA/N spleen cell colonies in vitro.

The expression of an X-linked defect in the CBA/N strain of mice has been found to result in a number of immune abnormalities. These include low responsiveness to antigens and a greatly reduced ability to respond to many of the common B cell mitogens. An in vitro manifestation of this condition is the virtual inability of CBA/N B cells to form colonies in lipopolysaccharide (LPS)-containing semisolid agar cultures. In this report we show evidence that the colony-forming ability of CBA/N spleen cells can be effectively restored by the bone marrow stromal-derived cell line S17. Spleen cells from 4-5-week-old homozygous CBA/N female mice were grown in double-layer agar cultures containing S17 feeder layers. Control cultures contained the fibroblast-like cell line 95.17 or were treated with medium alone. It was found that at an input cell concentration of 10(4) cells per plate, CBA/N colony formation was increased from a frequency of approximately 1 in 5,000 to 1 in 50 total splenic cells. Studies with purified surface immunoglobulin-positive cells indicate the direct involvement of S17 in this process. The CBA/N colonies formed were dependent on the presence of a mitogen (LPS) and secreted detectable amounts of IgM. Major implications of these findings and the application of this assay system to study the CBA/N defect have been discussed.

The B lymphocyte is the immune cell target for 2′,3′-dideoxyadenosine

2′,3′-Dideoxyadenosine (ddA) is a nucleoside analogue with anti-HIV activity and one of its metabolic products, 2′,3′-dideoxyinosine (ddI), has shown promising results in clinical trials for the treatment of acquired immunodeficiency syndrome (AIDS). Because AIDS viruses target the immune system, it is important to understand the potential effects of anti-AIDS drugs, including natural nucleosides, on the immune system. Previous immunotoxicological studies have shown that 22 treatments with ddA to female B6C3F1 mice over a period of 30 days had no effect on cell-mediated immunity, including the mixed lymphocyte reaction and response to mitogenic signals, but suppressed the in vitro IgM plaque-forming cell (PFC) response to sheep red blood cells. The present studies show that suppression of the IgM PFC response was dose dependent with a 96% reduction in IgM PFCs 10 6 spleen cells at the highest dose (350 mg/kg). The in vivo IgM PFC response to DNP-Ficoll and the in vitro IgM PFC response to lipopolysaccharide, both T-independent antigens, were also suppressed in the spleens of ddA-treated mice. The analysis of splenocyte subtypes shows no change in the percentage of B cells (surface immunoglobulin positive cells), T helper cells (L3T4 positive cells), and T suppressor cells or T cytotoxic cells (Lyt-2 positive cells) in the spleens of ddA-treated mice. In vitro separation and reconstitution studies in which the IgM PFC response was monitored indicated that the B lymphocyte rather than the T lymphocyte or antigen-presenting cell is the primary cell targeted by ddA. This information provides a data base for further mechanistic study and may reflect on the clinical use of other nucleoside analogues, e.g., ddI by providing the clinician with information indicating the potential decrease in humoral immunity.

Immunohistochemical study of insulitis induced by multiple low doses of streptozocin in CD-1 mice

In an attempt to characterize insulitis induced by multiple low doses of streptozocin (SZ), we immunohistochemically examined sequential changes of the subsets of lymphocytes infiltrating the pancreatic islets in CD-1 mice. Daily intraperitoneal injections of 30 mg/kg body wt of SZ for five consecutive days led to lymphocytic infiltration around the islets. Most of the infiltrated cells were initially CD4 positive (helper/inducer) T-lymphocytes and no immunoglobulin-bearing cells were detected. The number of helper/inducer T-lymphocytes increased with progression of the insulitis, then surface immunoglobulin-positive cells (B-lymphocytes) accumulated around the area of CD4 positive T-lymphocytes. CD8 positive (suppressor/cytotoxic) T-lymphocytes were seen scattered throughout the study and only a few asialo GM1 positive (natural killer) cells existed in the area of insulitis. Subsequently, the pancreatic insulin contents were considerably decreased and diabetes occurred on day 21. These observations suggest that CD4 positive T-lymphocyte-dependent B-lymphocyte infiltration in and around islet cells may be associated with islet cell destruction and the development of diabetes in CD-1 mice treated with multiple low doses of streptozocin.

Differential effects of a single dose of cyclophosphamide on T cell subsets of the thymus and spleen in mice: flow cytofluorometry analysis.

Sequential changes in the distribution of lymphocyte subpopulations of the thymus and spleen in BALB/c mice (male, 8-weeks old) during 2 weeks after a single i.p. injection of cyclophosphamide (CY, 200 mg/kg body weight) were studied mainly through the use of CD4, CD8 and CD3-epsilon markers together with single- or two-color flow cytofluorometry. In the thymus on Day 2 after CY treatment, a marked decrease in the number and proportion of PNAhi, CD3- and CD4+CD8+ double positive (DP) subpopulation was observed in parallel with a marked reduction in the thymus weight, cortical area and total thymocyte number. This phenomenon might be associated with the decrease in the percentage of thymocytes at the S phase of the cell cycle on Day 1 and 2 after CY treatment, owing to the depletion of the rapidly dividing cells in DP subset. There was a significant reduction in the number and proportion in CD4+ single positive(SP) subset on Day 7. The cell number of CD8+SP subset continued to decrease during Day 7 to Day 14. This contrasted with the behaviors of DP, CD4+SP and CD4-CD8- double negative (DN) subsets in which a considerable recovery was attained by Day 14. The spleen from CY-treated mice showed a marked decrease in the DN subset and surface immunoglobulin-positive cells, perhaps B lymphocytes, in both the percentage and the absolute cell number on Days 2 and 7, which paralleled the marked reduction in its weight and total cell number. The absolute cell numbers of CD4+SP and CD8+SP subsets in the spleen were also reduced on Days 2 and 7. The reduction of the CD4+SP/CD8+SP ratio was found in the thymocytes on Days 2 and 7 but not in spleen cells. Our results suggest that the principal target cell population of CY is the PNAhi, CD3- and DP immature cortical thymocytes as well as splenic B cells. The sustained decrease in the number of CD8+SP thymocytes after CY treatment might be in part relevant to the potentiating effect of CY pretreatment on immune responses.

Preparation and characterization of monoclonal antibodies against bovine B lymphocyte surface antigens

Two monoclonal antibodies (MoAbs; BLMo-4 and BLMo-10) were prepared by immunizing with a cell line established from peripheral blood mononuclear cells (PBMC) of enzootic bovine leukosis (EBL) cattle. The specificities of these MoAbs were assayed using bovine PBMC.BLMo-4 reacted with all surface immunoglobulin-positive cells (SIg + cells; B lymphocytes) and also recognized monocytes, but did not react with T lymphocytes. BLMo-10 recognized a majority, although not all, B lymphocytes, but did not react with either T lymphocytes or monocytes. The antigens recognized by BLMo-4 and BLMo-10 were not Ig, Fc or C3 receptors on the surface of B lymphocytes. The reactivity of the MoAbs with mononuclear cells from the lymphoid organs of adult cattle was studied. BLMo-4 and BLMo-10 did not react with any bone marrow cells. BLMo-10 reacted with 7.4% of thymocytes, and stained the medulla of the thymus in the immunoperoxidase assay. In the case of PBMC, spleen and lymph node cells, the percentage of cells positive for BLMo-4 was slightly higher than that of SIg + cells, but BLMo-10 showed a slightly lower value.

Immediate effects of intravenous IgG administration on peripheral blood B and T cells and polymorphonuclear cells in patients with myasthenia gravis.

Five patients with myasthenia gravis, who received treatment with intravenous 7S gamma-globulin were monitored for changes in immunological status. Serum immunoglobulin G increased from an average of 1.4 to 4.7 g/dl during the 5-day course of therapy. Specific antibody to the acetylcholine receptor present in three of five patients did not change. A transient decrease in total peripheral blood leukocytes was observed in five patients due to decreases in the absolute number of polymorphonuclear cells and lymphocytes in the circulation. Lymphocyte surface marker studies revealed that the percentage of surface immunoglobulin positive cells increased in all patients from an average of 13 to 26% by day 5 of therapy; however, the percentage of HLA-Dr- and Leu 12 (CD19)-positive B cells did not change. Lymphoid cells positive for the Leu 11 (CD16) marker doubled from an average of 11 to 24% during the 5-day course of therapy. Surface Ig-positive cells and Leu 11 (CD16)-positive cells returned to pretreatment values by 7 days posttherapy. Helper/suppressor cell ratios slowly decreased in all patients from an average of 2.9 to 2.2 by 1 week posttherapy and remained low for several weeks.

An analysis of the cellular requirements for the production of soluble interleukin-2 receptors in vitro.

Following activation in vitro, peripheral blood mononuclear cells (PBMC) express cell-associated interleukin-2 receptors (IL-2R) and also release soluble IL-2R into culture supernatants. The present studies were undertaken to define which normal cells were responsible for the release of soluble IL-2R in vitro. Both cell-associated and soluble IL-2R were quantitatively measured with a "sandwich" enzyme-linked immunoassay employing two monoclonal antibodies. PBMC were separated into populations of surface immunoglobulin-negative cells (T cells and monocytes) and surface immunoglobulin-positive cells (B cells and monocytes), and the T-cell population was further separated into OKT4-positive (OKT4+) cells and OKT4-negative (OKT4-) cells. Following activation with phytohemagglutinin, pokeweed mitogen, and the monoclonal antibody OKT3, large amounts of soluble IL-2R were released by PBMC, unseparated T cells, OKT4+ T cells, and OKT4- T cells. The population containing B cells and monocytes made small but readily detectable amounts of soluble IL-2R when stimulated with these T-cell mitogens; likely the result of contaminating T cells in the population. However, when highly purified B cells were stimulated with Staphylococcus aureus Cowan and recombinant IL-2, they also released small amounts of soluble IL-2R. The release of soluble IL-2R by T cells appeared monocyte dependent when OKT3, but not phytohemagglutinin, was employed for activation, and monocytes themselves released no detectable IL-2R under the conditions employed. These studies define the cellular requirements for the release of soluble IL-2R in vitro and demonstrate that such receptors are released by B cells, T cells, and both OKT4+ and OKT4- T-cell subsets.

Canine bronchoalveolar cells: antigen-presenting macrophages are Ia-positive, lymphocytes are of non-B lineage.

Subsegmental bronchoalveolar lavages were performed in 18 healthy beagles. The average yield per lavage was 45 X 10(6) cells consisting on the average of 24% lymphocytes, 71% macrophages, and 4% granulocytes. Cells were further examined in cytofluorometric studies using monoclonal (anti-Ia, antilymphocyte, anti-T) and polyspecific (anti-Ig) antibodies. Sixty to 90% of lymphocytes were T cells as determined by the T cell antibody DT-2. No surface immunoglobulin-positive cells (B cells) could be detected. All macrophages expressed Ia antigens (p 29/34) whereas lymphocytes did not. In assays of concanavalin A-induced blastogenesis of thymocytes, alveolar macrophages functioned as accessory cells. The anti-Ia antibody 7.2 interfered with this function, indicating that Ia antigens on canine alveolar macrophages are involved in interaction with T cells resulting in T cell proliferation.

Cytofluorographic analysis of pokeweed mitogen-stimulated human peripheral blood cells in culture: age-related characteristics.

By use of monoclonal antibodies and flow cytometry techniques, peripheral blood mononuclear cells from young (20-30 years) and elderly (70+ years) subjects were analyzed before and after culture with pokeweed mitogen to gain insight into the cellular interactions responsible for the decreased B cell response observed in culture samples from the elderly. Data analysis of surface immunoglobulin-positive cells demonstrated no difference in the percentage of B cells in the elderly, while both plaque-forming cell and intracytoplasmic immunoglobulin assays showed significantly reduced B cell maturation (P = less than 0.01) compared with young controls. The B cell defect was shown to be functional and not a result of failure to proliferate and survive during incubation. Surface marker analysis of T cell subpopulations demonstrated a definite shift (P = less than 0.01) in the helper/suppressor T cell ratio in cultured samples from the elderly group (3.9) compared with young subjects (1.2). In addition to the absolute increase in the helper T cell population, forward-angle light scatter analysis demonstrated that, compared with young controls, a greater portion of the helper T cell population in the elderly subjects had characteristics of activated, blast-sized cells. The data reported in this study suggest that in the elderly group there is a functional immunoregulatory imbalance in the helper T cell subset.

Lymphocyte subpopulation changes by aging

Peripheral blood lymphocyte suspensions of healthy young and aged subjects were tested for the percentage of (1) E-rosetting cells by three different modifications of the rosette technique; (2) α-naphthylacetate esterase positive cells of different staining patterns; (3) IgG-Fe receptor positive cells; (4) C3 receptor positive cells; (5) labile and stable bound surface immunoglobulin positive cells; and (6) cells bearing different classes of immunoglobulins on their surface or intracytoplasmically. Age dependent changes were registered both within the T-cell and the B-cell subpopulations, some of which may be due to in vivo activation of lymphocytes. Attention is called to some technical aspects of lymphocyte subpopulation determinations and to the significance of quantitative changes in the proportions of lymphocyte subpopulations in respect to the age dependent functional changes of lymphocytes.

Mechanisms of cellular cytotoxicity mediated by effector cells from rats with spontaneous tumors.

We have previously shown that effector cells from BD X rats bearing spontaneous tumors display increased cytotoxicity towards syngeneic tumor cells compared to effector cells from untreated rats (Zöller and Matzku, 1980 a). The increased in vitro cytotoxicity of lymphoid cells from tumor-bearing (TB) animals was not T-cell mediated and the question was raised, whether it was due solely to increased natural killer (NK) cell activity, or whether humoral factors could also be involved. We now prove that in a long-term assay, the presence of B cells is indeed mainly responsible for increased TB cytotoxicity, since: (1) After depletion of surface immunoglobulin positive cells (s-Ig+), TB cytotoxicity no longer exceeds cytotoxicity of effector cells from untreated rats; (2) Mixtures of s-Ig+ cells from TB animals with Fc-receptor positive (Fc-R+) cells from untreated rats restore the increased TB cytotoxicity; (3) Addition of rabbit Fab' anti rat F(ab')2 reduces TB-effector cell cytoxicity. A minor contribution of the increased TB cytotoxicity by activation/numerical increase of NK cells will be discussed.