Natural cytotoxicity in rats: Radiation-induced changes in the early killing of allogeneic cells

In some strain combinations among inbred tats intravenously injected ⁵¹Cr-labeled lymphocytes are rapidly destroyed in substantial numbers by unsensitized allogeneic hosts. This phenomenon has been referred to as natural cytotoxicity (NC) and is characterized by decreased lymph node radioactivity, increased kidney and urine radioactivity, and to a lesser extent increased liver radioactivity in allogeneic hosts, when compared with the distribution of label in syngeneic recipients of the same cell suspension. A single exposure to 800 rad either 1 or 7 days before the injection of ⁵¹Cr-labeled lymphocytes effected a reduction in NC as defined by all the above parameters in a strain combination exhibiting high NC. The same dosage of radiation abolished NC in a strain combination exhibiting intermediate → low NC. Because NC was not always completely abolished, the phenomenon was held to be partially radiosensitive. An increased accumulation of ⁵¹Cr-labeled lymphocytes was seen in the lymph nodes of both syngeneic and allogeneic irradiated hosts when compared with nonirradiated controls, although the increase was greater in allogeneic than in syngeneic hosts. This increased colonization in the lymph nodes of irradiated hosts seemed unlikely to be due to an increase in the available “space” in the lymph nodes following irradiation.     

Evaluation of in vitro cytotoxic T lymphocyte assays as a predictive test for the occureence of graft vs host disease

The potential value of in vitro cytotoxic T lymphocyte (CTL) assays for predicting the occurrence of graft vs host disease (GVHD) following allogeneic bone marrow transplantation was evaluated in 12 mouse donor-host combinations associated with various degrees of GVHD. These donor-host combinations were selected after evaluation of GVHD triggered by minor histocompatibility antigens (MiHA) in 24 allogeneic strain combinations derived from six strains of H-2 ^b mice. Recipients (n=475), previously submitted to total body irradiation (9.5 Gy), were transplanted with 10⁷ bone marrow cells along with 5 x 10⁷ spleen cells. While lethal GVHD was observed in half of the strain combinations, it was possible to select 12 donor-host combinations characterized by severe, mild, or absent GVHD. When levels of anti-host CTL activity were assessed following in vivo priming and in vitro boosting, strong CTL-mediated cytotoxicity was observed in all combinations wheteer they developed GVHD or not. CTL frequency measured by limiting dilution analysis (LDA) ranged from 1/16880-1/306. The Spearman rank test revealed no positive correlation between GVHD intensity and donor anti-host CTL activity assayed either in bulk culture experiments or in LDA conditions. These results indicate that MiHA capable of triggering potent CTL responses in vitro do not necessarily initiate GVHD, and that in vitro measurement of donor CTL activity against host-type Con A blasts is not a predictive assay for anti-MiHA GVHD. However, the possibility to recruit CTL populations targeting host MiHA expressed specifically on hematopoietic cells suggests a novel therapeutic strategy for the cure of hematopoietic malignancies. Indeed, transplantation of donor hematopoietic stem cells supplemented with T cells aimed at MiHA specifically expressed by host hematopoietic cells, could possibly potentiate the desirable graft vs leukemia effect without increasing the risk of GVHD.     

Effect of aging on T-cell tolerance induction

In the MHC compatible rat strain combination AS → HS, the same ⁵¹Cr-labeled lymph node suspension behaves totally differently depending on whether it is injected into syngeneic or allogeneic recipients. Using ⁵¹Cr-labeled lymph node suspensions from AS or (AS × HS)F1 donors, and AS, HS, and F₁ hosts, the distribution of label over a 72-hr period was studied. Evidence has been obtained that recognition of self-components results in the homing of cells to the lymph nodes in syngeneic hosts, while recognition of foreignness impairs homing of the same cells to the lymph nodes in allogeneic hosts. The spleen is the major organ in which these recognition processes occur. Substantially more cells are destroyed by nonimmune allogeneic hosts than by syngeneic hosts, a clear difference being apparent as early as 6 hr after injection. Some lymphoid cells are obligatory spleen seekers and do not enter the lymph nodes.     

Specific inhibition of natural killer (NK) activity against different alloantigens

Allogeneic lymphocyte cytotoxicity (ALC), i. e., rapid rejection of i. v. injected allogeneic lymphocytes in unprimed hosts, is an example of NK activity. Apparently anomalous rejection patterns, such as acceptance of F₁ hybrid cells by parental hosts and rejection of parental cells by F₁ hybrid hosts in many strain combinations, would fit the hypothesis that the effector cells in ALC recognize the absence of certain self-molecules (passwords) rather than the presence of nonself determinants. However, cold target inhibition studies showed that ALC displays allospecificity: when a mixture of radiolabeled AO and DA cells were injected i. v. into euthymic or athymic PVG rats, adding a surplus of cold DA cells reduced killing only of labeled DA cells and vice versa. Furthermore, semiallogeneic cold target cells were ineffective in inhibiting elimination of fully allogeneic cells, which supports the argument against a modification of the hypothesis that self-determinants inhibit a postbinding stage of lysis. Finally, (DA × AO)F₁ cells injected into (DA × PVG)F₁ hosts were rapidly rejected, despite the fact that donor and host shared expressed DA determinants. In sum, our results show that a hypothesis based on inhibition of killing by self-determinants can only be sustained with extensive modifications, and favor the alternative mechanism that the effector cells positively recognize the presence of allospecific determinants on the target cell surface.     

The influence of strong transplantation antigens (Ag-B) on lymphocyte migration in vivo.

The tissue localization of syngeneic thoracic duct lymphocytes was compared to that of allogeneic cells in four rat strain combinations differing at the Ag-B locus (HO → DA, DA → HO, AO → HO, HO → AO). Dual isotope labeling with [³H]uridine and [¹⁴C]uridine was applied in order so that the distribution of allogeneic and syngeneic cells could be followed in one recipient. During the first couple of hours after iv injection, allogeneic lymphocytes usually migrated as easily into the various tissues as did syngeneic cells. However, after 24 and 48 hr, a reduced amount of label associated with allogeneic cells was often measured in the tissues. This reduction differed in magnitude in the different strain combinations and was most pronounced in the lymph nodes. A reduced number of allogeneic cells also appeared in the thoracic duct. By contrast, no reduced localization of allogeneic lymphocytes was measured in the draining popliteal lymph nodes late after sc injection. In preimmunized animals allogeneic cells were rapidly removed from the blood and therefore failed to localize in the lymphoid tissues. Furthermore, the lymph node localization of allogeneic cells was more like that of syngeneic cells in splenectomized rats, as well as in irradiated recipients (when the irradiation was given shortly before cell transfer). It is concluded that transplantation antigens play no essential role in the interaction between recirculating lymphocytes and the venous endothelium at the sites where the large-scale physiological emigration of the cells takes place (the HEVS of the lymph nodes and the marginal zone vessels of the spleen). The elimination of allogeneic cells is found later; it probably takes place in the lymph nodes and spleen. Possible mechanisms responsible for this rapid removal of allogeneic lymphocytes in nonimmunized recipients are discussed.     

Functional analysis of mononuclear cells infiltrating into tumors. II. Differential ability of mononuclear cells obtained from various tissues to produce helper factors that are involved in the generation of cytotoxic cells

The requirement of CGF in the generation of cytotoxic cells against syngeneic tumor cells (T-9) and in the rejection of transplanted T-9 cells has been investigated. Spleen cells obtained from sensitized rats showed strong cytotoxicity against 51Cr-labeled T-9 cells upon incubation with CGF for 48 hr. Human recombinant IL 2 and rat IFN failed to generate cytotoxic cells from spleen cells of sensitized rats. CGF are produced by spleen cells upon inoculation of T-9 cells into sensitized rats as a host in vivo immune response. Production of CGF preceded the appearance of cytotoxic cells in regional lymph node and tumor tissues. In those rats, inoculated tumor cells were eventually rejected. In contrast, spleen cells failed to produce CGF upon inoculation of T-9 cells in unsensitized rats. Cytotoxic cells were not detected in unsensitized rats, and inoculated tumor grew in those rats. Thus, CGF is likely to be involved in the generation of cytotoxic cells and in the rejection of inoculated syngeneic tumor cells. A Mono Q anion-exchange column with an FPLC system allowed the chromatographic separation of CGF from IL 1, IL 2, IL 3, and CSF.     

Single and multiple congenic strains for hydrocephalus in the H-Tx rat

The H-Tx rat has fetal-onset hydrocephalus with a complex mode of inheritance. Previously, quantitative trait locus mapping using a backcross with Fischer F344 rats demonstrated genetic loci significantly linked to hydrocephalus on Chromosomes 10, 11, and 17. Hydrocephalus was preferentially associated with heterozygous alleles on Chrs 10 and 11 and with homozygous alleles on Chr 17. This study aimed to determine the phenotypic contribution of each locus by constructing single and multiple congenic strains. Single congenic rats were constructed using Fischer F344 as the recipient strain and a marker-assisted protocol. The homozygous strains were maintained for eight generations and the brains examined for dilated ventricles indicative for hydrocephalus. No congenic rats had severe (overt) hydrocephalus. A few pups and a significant number of adults had mild disease. The incidence was significantly higher in the C10 and C17 congenic strains than in the nonhydrocephalic F344 strain. Breeding to F344 to make F.H-Tx C10 or C11 rats heterozygous for the hydrocephalus locus failed to produce progeny with severe disease. Both bicongenic and tricongenic rats of different genotype combinations were constructed by crossing congenic rats. None had severe disease but the frequency of mild hydrocephalus in adults was similar to congenic rats and significantly higher than in the F344 strain. Rats with severe hydrocephalus were recovered in low numbers when single congenic or bicongenic rats were crossed with the parental H-Tx strain. It is concluded that the genetic and epigenetic factors contributing to severe hydrocephalus in the H-Tx strain are more complex than originally anticipated.     

Genetics of a non-H-2 antigen that stimulates "unrestricted" helper T cells and MLR

The inheritance of antigens expressed by C3H/Tif B cells that stimulate MHC-unrestricted helper T cells from C3H/HeJ was investigated. F1 hybrids between C3H/HeJ and C3H/Tif and 39 C3H/HeJ X F1 backcross mice were characterized as to the ability of their spleen cells to stimulate a proliferative C3H/HeJ T helper cell response and to respond to helper cell activity by the development of polyclonal plaque-forming cell responses. Backcross progeny wee also typed for the following markers segregating in this cross: 1) Responsiveness to the B cell mitogen lipopolysaccharide (LPS); 2) LyM-1 allotype; 3) antigen(s) stimulating a primary non-H-2 MLR between these strains, previously ascribed to Mls locus differences, 4) expression of target antigens for cytotoxic T cells raised in the same strain combination. The antigen(s) recognized by helper cells and those stimulating primary MLR are controlled by autosomal gene(s) and segregate as a single trait. These antigens, however, are not encoded in genes linked to either the Lps or the Mls loci, and are not recognized by cytotoxic T cells raised in the same strain combination.     

Natural cytotoxic autoantibody against thymocytes in spontaneously hypertensive rats

A strain of SHR rats, which spontaneously develops hypertension and periarteritis nodosa, had a decreasing number of rosette-forming T cells in their thymuses and a progressive decline in cellular immune functions by aging. They were found to produce natural thymocytotoxic autoantibody (NTA) detected by a complement-dependent cytotoxicity test. This autoantibody occurred from 1 month of age and throughout life; the incidence was more than 60% of SHR rats at any age. Thymocytes from all six rat strains tested showed similarly high sensitivity to NTA but none of the strains tested produced NTA except the SHR strain. Rosette-forming thymocytes of WKA rats, which were separated by Ficoll gradient, showed much higher cytotoxic sensitivity to NTA than did whole thymocytes and nonrosetting thymocytes. The cytotoxicity of NTA was weak or negative for spleen cells, lymph node cells, bone marrow cells, and blood lymphocytes of WKA rats. However, the cytotoxic activity of NTA was completely absorbed with the thymus, spleen, lymph node cells, and brain homogenates and was partially absorbed with bone marrow cells, but not with liver and kidney homogenates. NTA in SHR rats was an IgM-globulin as determined by sensitivity to 2-ME treatment and by Sephadex G-200 column chromatography. These results suggest that NTA is responsible for the selective suppression of T-cell functions in SHR rats.     

Graft-versus-host response,measured by splenomegaly assay,by populations of allosensitized mouse lymphocytes

The graft-vs-host (G-v-H) reactivity of sensitized or nonsensitized mouse lymphoid cell populations was measured using a splenomegaly assay. Sensitized populations were obtained either from the local lymph nodes of alloimmunized animals or from the spleens of heavily irradiated mice previously infused iv with allogeneic lymphocytes (educated cells). Immunization of animals resulted in increased G-v-H responses of the cells in their local lymph nodes. This effect was more pronounced when the immunizing cells differed only at non-H-2 transplantation antigens than when H-2-disparate strain combinations were tested. There was no evidence of a changed doseresponse profile of lymphocytes obtained from immunized mice. The G-v-H reactivity of educated cell populations was complex. The slopes of the dose-response lines obtained for lymph node cells or thymic cells educated in an H-2-disparate strain were generally lower than those obtained for nonsensitized cells. This difference was particularly evident when testing educated thymocytes. By studying the G-v-H indices obtained in A/Sn × C57B1 hybrids after inoculation of nonsensitized C57B1 lymph node cells or specifically educated C57BL lymph node cells, it was observed that the latter cells were approximately 30 times more reactive when small cell inocula were compared. On the contrary, education of lymphocytes in H-2-compatible allogeneic hosts did not result in any increment of their G-v-H reactivity. The results indicate that different methods of sensitizing lymphocyte populations against alloantigens may lead to activation of different subclasses of T-cells which differ in their mode of antigen reactivity.     

Generation of a polymorphic marker linked to thymoma susceptibility gene of rat 1 by genetically-directed representational difference analysis.

BUF/Mna (BUF) is a rat strain susceptible to spontaneous development of thymomas. We have previously shown that the thymoma susceptibility is controlled principally by a dominant susceptibility gene located on chromosome 7, thymoma susceptibility gene of rat 1 (Tsr1). To generate genetic markers tightly linked to Tsr1, we performed genetically directed representational difference analysis (GDRDA) with three combinations of the tester and driver DNAs. From 124 ?ACI/NMs x (BUF x ACI/NMs) F1? backcross rats, 12 rats with the ACI/BUF genotype in the Tsr1 region (A/B rats) and 13 rats with the ACI/ACI genotype in the region (A/A rats) were selected, and their DNAs were pooled, respectively. Three kinds of tester DNAs, i) inbred BUF, ii) (BUF x ACI)F1, and iii) the pool from the A/B rats, were subtracted by the driver DNA prepared from the pool of the A/A rats. The three combinations yielded one, two, and one polymorphic marker(s), respectively. One marker, D7Ncc28, was isolated commonly by the three combinations of subtraction, and another marker, D11Ncc12 was isolated only by the second combination. Linkage analysis demonstrated that D7Ncc28 was located in the 8.3 cM region where Tsr1 has been mapped. The three combinations of subtraction were shown to be almost equally capable of isolating polymorphic markers in a specific chromosomal region.     

Antigen presentation by Langerhans cells in vivo: donor-derived Ia+ Langerhans cells are required for induction of delayed-type hypersensitivity but not for cytotoxic T lymphocyte responses to alloantigens

T cell activation in response to allogeneic stimulation and hapten-specific delayed-contact hypersensitivity responses in vivo can be initiated by Ia-bearing epidermal Langerhans cells (LC). By using a murine heterotopic corneal allograft model, we have investigated the requirement for allogeneic LC as antigen-presenting cells (APC) in the in vivo induction of delayed-type hypersensitivity (DTH) and cytolytic T lymphocyte (CTL) responses to alloantigens in fully allogeneic and H-2 I region-disparate strain combinations. LC-deficient, avascular central corneal allografts from BALB/c donors failed to induce DTH responsiveness when grafted to a subdermal bed on C57BL/6 recipients (p greater than 0.05), yet antigen-specific primary CTL reactivity developed within 7 days after grafting. LC-containing corneal-limbus allografts or central corneal allografts containing a latex bead-induced infiltrate of LC resulted in intense DTH as well as CTL responsiveness when grafted in this same strain combination. Similarly, LC-containing but not LC-deficient corneal allografts from A.TL donors induced DTH responsiveness in I region-disparate A.TH hosts despite the fact that these grafts survived for prolonged duration (less than 28 days). By contrast, CTL induction in I region-disparate hosts was independent of the presence of allogeneic LC. Corneal epithelial cells of grafts removed from I region-disparate hosts 7 days posttransplantation were shown by immunohistology to express the Iak antigens of donor origin. The possibility that bone marrow-derived allogeneic LC were a sufficient requirement for DTH induction was confirmed in experiments performed with CB6F1----B6 bone marrow chimeras used as corneal allograft donors. Corneal-limbus grafts obtained from mice 90 days after chimerization were shown by immunohistology to contain Iad-bearing CB6F1 LC as a sole source of class II alloantigens. When grafted to C57BL/6 recipients, LC-containing chimeric corneas induced DTH responsiveness that was similar in magnitude to that observed in C57BL/6 mice grafted with chimeric skin, yet no DTH response to LC-deficient chimeric central corneal grafts was observed. Moreover, in all cases, the chimeric corneal and skin allografts survived for prolonged duration (greater than 28 days). These results demonstrate that donor-derived LC act as APC in the induction of DTH responsiveness to allogeneic tissue; however, there was no apparent requirement for allogeneic LC in the induction of CTL responses to class I or class II MHC alloantigens.(ABSTRACT TRUNCATED AT 400 WORDS)     

A Dominant Gene for Male Sterility in Salvia miltiorrhiza Bunge

A natural male sterile mutant of Salvia miltiorrhiza (Labiatae, Sh-B) was found during field survey in 2002. Our objective was to analyze its genetic mechanism for producing F1 hybrid seeds and to develop a molecular marker linked to male sterile gene for selection of a hybrid parent line. The segregation ratios of male sterile plants to fertile plants in the progenies of both testcross and backcross were 1:1 in continuous experiments conducted in 2006–2009. The male sterile Sh-B was heterozygous (Msms). The male sterile plants could capture most pollen (2 granule/cm²·24 h) with row ratio (female : male 2 : 1) within 45-cm distance and harvest the largest amount of 6495 g hybrid seeds per hectare. We also developed DNA markers linked to the male sterile gene in a segregating population using bulked segregant analysis (BSA) and amplified fragment length polymorphism (AFLP) techniques. The segregating population was subjected to BSA-AFLP with 128 primer combinations. One out of fourteen AFLP markers (E11/M4208) was identified as tightly linked to the dominant male sterile gene with a recombination frequency of 6.85% and at a distance of 6.89 cM. This marker could be converted to PCR-based assay for large-scale selection of fertile plants in MAS (marker-assisted selection) at the seedling stage. Blastn analysis indicated that the male sterile gene sequence showed higher identity with nucleotides in Arabidopsis chromosome 1–5, and was more likely to encode S-adenosylmethionine-dependent methyltransferase, in which DNA methylation regulated the development of plant gametogenesis.     

Failure of ovalbumin associated with allogeneic spleen ceels to stimulate proliferation of lymph node cells of immune mice.

Ovalbumin-pulsed spleen cells were found to stimulate thymidine uptake of lymph node cells of syngeneic mice immunized with ovalbumin in complete Freund's adjuvant after treatment of spleen cells with Mitomycin C but not after heating the spleen cells at 56degrees for 30 min. Ovalbumin-pulsed spleen cells of allogeneic mice failed to stimulate the immune lymph node cells more than unpulsed cells, although a net increase in the thymidine uptake above the allogeneic stimulation was observed when free ovalbumin was added to the mixed culture. To eliminate the high background of the mixed lymphocyte reaction, F1 mice were made chimeric with bone marrow of one of the parental strains. Using lymph node cells of the immunized chimeras, the stimulation by pulsed spleen cells was much greater when antigen was presented on cells of the parental strain used for bone marrow injection than when presented on cells of the other parental strain.     

Genetic association between low expression phenotype of CD62L (L-selectin) in peripheral CD4+ T cells and the thid (T-helper immunodeficiency) phenotype in the LEC rat.

Genetic linkage analysis was performed between the low expression phenotype of peripheral CD4+ T cells and the thid (T-helper immunodeficiency) phenotype using (BN x LEC)F1 x LEC backcross progenies. In contrast to a previous result using a thid congenic strain that the low expression phenotype of CD62L was not correlated with the thid phenotype, our result in this study indicated that the low expression phenotype of CD62L was genetically linked with the thid phenotype. The discrepancy between the previous and present results may be due to the source of animals, congenic strain versus backcross progenies. It is suggested by this study that the thid locus controls the expression level of CD62L in peripheral CD4+ T cells.     

The screening of non-H-2 congenic lines forSk loci

Thirty-seven histocompatibility congenic lines of mice, including at least 27non- H-2 lines, developed by Bailey on the C57BL/6 background, were screened for loci determining Sk (skin-specific) histocompatibility antigens. Background strain hosts were inoculated with lymphoid cells from the congenic lines and subsequently challenged with skin test grafts from the same donors. Comparison of the survival times of these test grafts with those of first- and second-set skin grafts in the same donor-host combinations suggests that the lymphoid cells from 35 of the congenic lines apparently immunized or tolerized at least some of the hosts. Thus, the histocompatibility antigens involved were shared by lymphoid cells and skin, and by definition could not be Sk antigens. The tests were indecisive with two of the non-H-2 lines, but if Sk antigens were involved, their contribution to the immunogenicity of conventional skin allografts probably was negligible. Hence ifSk congenic lines are desired, they probably will have to be developed on their own by procedures specifically designed to select for Sk antigens of significant immunogenicity.     

大白菜细胞核复等位雄性不育基因定位

以大白菜不育材料"939A"为母本,携带恢复基因的材料YDQ56A为父本构建隐性雄性不育F1S4分离群体,利用混合分组分析法(BSA)对不育基因初定位;同时以"939A"为母本,携带保持基因的材料yellow sason为父本构建显性雄性不育F2分离群体,对不育基因进行精细定位。结果在F1S4群体中获得与不育基因连锁的标记2个,A08_1900和Br ID111035,与不育基因分别相距8.8c M和2.5c M,物理距离为804.1kb;F2群体中不育单株与可育单株分离比符合3∶1,不育基因表现为显性。通过标记验证,F2和F1S4两个群体定位结果一致,均位于A08染色体末端,通过新标记的筛选获得不育基因两侧紧密连锁的标记Br19470306和Br19675586,与不育基因分别相距1.6c M和2.4c M,物理距离205.28kb,其中包含58个基因。该结果为大白菜雄性不育系的利用以及转育奠定了基础。     

Restriction by the major histocompatibility complex of antigen-induced T lymphocyte proliferation in new inbred guinea pig strains.

Employing new inbred guinea pig strains, JY 1, JY 2 and JY 3, established in this Institute in addition to strains 2 and 13, the authors investigated histocompatibility restriction in macrophage-T lymphocyte interaction. These five strains are known to possess distinct major histocompatibility complex (MHC) gene profiles (1, 2). This fact was supported by our results concerning the mixed leukocyte reaction (MLR) and cytotoxicity test with alloantisera. Using various combinations of T lymphocytes and peritoneal exudated cells (PECs) from these strains, in vitro proliferative responses of T lymphocytes from BCC-immune animals to PPD-pulsed normal PEC were tested. Successful activation of T cell response was observed not only in syngeneic combinations but also in allogeneic combinations among strains JY 1, JY 3 and strain 13 which share common Ia antigens detected by strain 2 anti-strain 13 alloantiserum. Because JY 1 and JY 3 seem to share a common B antigen differing from strain 13, it was suggested that identification in the I region of MHC is sufficient for effective antigen-presentation by the macrophage. Although a part of Ia is shared, no T lymphocyte activation was observed in the combination between JY 2 and JY 1 or JY 3, whereas strong MLR occurred in these allogeneic combinations. At the present stage of the study, it can be said that disparity in the part(s) of Ia antigens which is responsible for strong MLR cannot lead to effective T cell-macrophage interaction. These results support the concept that functional activation of primed, proliferating T lymphocyte requires the participation of gene products of macrophages coded for by the I region in MHC. By employing JY 1, JY 2 and strain 2, which appear to possess distinct B and Ia antigens, it was shown that the T lymphocyte and macrophage interactions essential for mitogen-induced T lymphocyte proliferation are not restricted by histocompatibility.     

Peyer's patch lymphocytes express natural cytotoxicity but not natural killer activity

The distribution of natural cytotoxic (NC) cells in the gut-associated lymphoid tissues (GALT) and in peripheric lymphoid organs was analyzed in comparison to that of natural killer (NK) cells. It was found that cells from the intestinal epithelium, mesenteric lymph nodes and spleen possess significant levels of NC and NK activity, whereas in thymus and popliteal lymph nodes both the natural activities are negligible. As previously shown for splenocytes, the NC activity of GALT cells is detectable in the 16-hour assays and not in the 4-hour assays. Interestingly, Peyer patches lymphocytes (PPL) possess extremely high NC activity but no NK activity. The NC activity of PPL is still high in NK-deficient mouse strains such as A/J and SJL/J. To further support the observation that the effector PPL are truly NC cells, it was shown that, as previously reported for spleen NC activity, overnight incubation at 37 degrees C of the lymphocytes only marginally affected the cytotoxicity of PPL, which could in turn be augmented by interleukin-3 (IL-3) containing supernatants. On the contrary, IL-2 could not increase NC or NK activity by PPL whilst augmenting NK activity of splenocytes. Thus, for the first time a cell population is identified which expresses only NC activity and not NK and which can be positively regulated only by IL-3.