Initial nonfunction in cadaveric renal transplantation

Patients who receive a kidney transplant that does not function immediately have more complications and decreased graft survival than patients whose allografts function immediately. To determine the causes of initial nonfunction (INF), the authors reviewed 188 consecutive cadaveric kidney transplants performed between 1985 and 1988 at the University Hospital, London, Ont. Data were collected on 16 putative risk factors for INF, which were divided into three categories: donor, recipient and technical. INF was defined as the need for dialysis within 7 days of transplantation. Forty-eight (26%) of the 188 allografts had INF, 6 of which never functioned. Univariate analysis identified five variables associated with increased risk of INF: no donor dopamine use, back-table flush, single-organ retrieval, exchanged kidney and prolonged cold ischemic time. Multivariate analysis, however, identified only three variables associated with INF: cerebrovascular accident as the cause of donor death, no donor dopamine use and single-organ retrieval. The authors recommend (a) low-dose dopamine therapy for all donors and (b) multiorgan retrieval to produce quality kidneys for transplantation.

Ro/SSA inhibits the autologous mixed lymphocyte reaction

To test the hypothesis that the Ro/SSA autoantigen can be recognized as antigenic by the human immune system, lymphocytes obtained from normal volunteers were used in in vitro assays evaluating the ability of Ro/SSA (mol. wt 60 kD) to induce B and/or T cell responses. Bovine Ro/SSA strongly inhibited the autologous mixed lymphocyte reaction in a dose-dependent manner without similar effects on concurrently performed allogeneic mixed lymphocyte reactions or T cell proliferation induced by phytohaemagglutinin. Using three colour FACS analysis, Ro/SSA was found to decrease the percentage of CD4+CD45+RA+ T cells in the proliferative, S+(G2+M), phase of the cell cycle. Associated with the decrease in the percentage of suppressor-inducer cells, was the finding that Ro/SSA was able to augment RF production in pokeweed mitogen stimulated cultures of peripheral blood lymphocytes.

INHIBITION OF ALLOREACTIVITY IN VITRO BY MONOCLONAL ANTIBODIES DIRECTED AGAINST RESTRICTED ISOFORMS OF THE LEUKOCYTE-COMMON ANTIGEN (CD45)

The leukocyte common antigen (LCA) is a protein tyrosine phosphatase and is identified by the CD45 cluster of monoclonal antibodies. CD45 is expressed in high-density on cells of hematopoietic lineage and generally is immunoprecipitated as 4 bands (220, 205, 190, and 180 KDa). Genetic studies have shown that a single gene produces additional forms of the molecule by alternate splicing including CD45RA (220, 205), CD45RO (180), and CD45RB (220, 205, 190). We have prepared a CD45RB Mab termed "MT3" that binds to a sialic acid dependent epitope. Since the LCA is one of the major targets of antilymphocyte globulin, we assessed a panel of CD45 and CD45R Mab for their ability to inhibit alloreactivity in vitro. MT3 (CD45RB) inhibits the allogeneic MLR and inhibits CD4+ T cells from expressing interleukin 2 receptors, and prevents CD4+ CD45RA- T cells from entering the proliferative phase of the cell cycle. Mem 93 (CD45RA) inhibits the generation of cytotoxic T cells. These data suggest that the CD45RB and CD45RA isoforms of the LCA may be appropriate targets for in vivo immunotherapy.

The outcome of pregnancy following renal transplantation--the experience of a single center

Many centers still recommend avoidance of pregnancy after renal transplantation because of fears for the safety of both mother and fetus. These fears are in part based on a lack of information concerning the effects of newer immunosuppressive drugs such as cyclosporine on the course and outcome of pregnancy. The present study examines the experience of first pregnancies following renal transplantation in a single center, with emphasis on the role of CsA. Data on the first pregnancies of 22 women transplanted between 1977 and 1988 were studied. The mean age of patients at the time of transplant was 23.4 +/- 3.1 years and interval from transplant to pregnancy was 34.5 +/- 24.5 months (range 1-75 months). Twelve patients received CsA alone or in combination with other immunosuppressives, while the remaining 10 patients received azathioprine and prednisone. Mean serum creatinine fell progressively during pregnancy in both CsA- and azathioprine-treated mothers. Mean CsA dose rose during pregnancy while mean CsA blood concentration fell during the 2nd trimester (P = 0.042). The gestation period ranged from 27 to 40 weeks (35.5 +/- 3.3) with 14 pregnancies ending prematurely prior to 37 weeks. Thirteen deliveries occurred by Caesarian section. Hypertension complicated 10 pregnancies. Birth weight correlated directly with both maternal weight gain (r = 0.57; P less than 0.02) and gestational age (r = 0.9; P less than 0.01). Ten of 23 offspring were below the 10th percentile for weight. Mean birth weight ranged from 0.72 to 3.7 kg (2.3 +/- 0.84 kg). The mean birth weight and gestational age of children born to mothers taking CsA were lower than those in azathioprine treated mothers but these differences were not statistically significant. Successful pregnancy is possible following renal transplantation, although there is a high rate of prematurity, low birth weight, and intrauterine growth retardation. CsA dose requirements may be increased. Maternal risks including hypertension require that such pregnancies be handled by a multidisciplinary team approach.

Living Related Kidney Donors: Historical and practice perspectives

A kidney transplant is the treatment of choice for suitable patients with end-stage renal disease. The living related kidney donor represents an important source of kidneys because graft survival is much better and there is a critical shortage of organ donors. This article reviews the risks to the donor and the means by which these individuals are assessed in order to minimize the risk.

CD7- T cells in rheumatoid arthritis

OBJECTIVE

Rheumatoid arthritis (RA) is characterized by decreased expression of CD7 in the peripheral blood and in the synovium. The present study was designed to identify the basis for and functional consequences of this decreased expression.

METHODS

Peripheral blood lymphocytes from normal controls and from patients with RA or systemic lupus erythematosus (SLE), and T cell lines derived from rheumatoid synovium, were evaluated using 3-color fluorescence-activated cell sorter analysis.

RESULTS

Normal subjects and most SLE patients expressed homogeneous, bright CD7 on CD4+, CD45RA+ cells, whereas RA patients demonstrated a significantly increased proportion of CD7- cells. T cell lines derived from rheumatoid synovium demonstrated a striking deficiency of CD7 on CD4+, CD45RA- cells. CD4+, CD45RA+ cells from RA patients changed phenotype after in vitro activation to CD45RA negativity, with up-regulation of CD7. CD7-, CD4+, CD45RA- cells were assessed for their ability to induce pokeweed mitogen-driven IgM and IgM-rheumatoid factor synthesis, and they were found to be potent helper/inducer cells. An increased population of CD7-, CD4+ cells in peripheral blood was found to predict a low response to recall antigens.

CONCLUSION

The low expression of CD7 in RA may explain some of the immune abnormalities which may contribute to the pathogenesis of this disease.

Mechanisms of rejection during OKT3 therapy: propagation and characterization of CD3 resistant allospecific cytotoxic T cells from a rejecting liver allograft

Allograft rejection remains the single largest impediment to success in the field of transplantation. While OKT3 therapy has proven to be a significant advancement, many grafts are still lost. Late treatment, subtherapeutic OKT3 levels, anti-OKT3 antibodies, and OKT3-induced class II antigen expression are possible explanations. To determine the mechanism of OKT3 resistant rejection we propagated and characterized infiltrating T cells from the biopsy of a liver transplant patient who was rejecting while on prophylactic OKT3. The T lymphocytes demonstrated allospecific proliferation and interleukin 2 (IL2) production and showed a high degree of cytolysis of donor splenocytes. CD3 epsilon monoclonal antibodies (Mab) in concentrations up to 100 micrograms/ml did not inhibit lysis. In contrast, T lymphocytes derived from rejecting allografts of patients receiving cyclosporine and prednisone were readily inhibited from killing by CD3 epsilon Mab at doses of 1 microgram/ml. Furthermore, allospecific proliferation and IL2 production were not inhibited in the OKT3-treated patient by the addition of CD3 epsilon MaB. Incomplete modulation of the CD3-TCR complex was noted after a 72-hr incubation with CD3 epsilon Mab. The T cells did demonstrate other intact CD3-mediated functions such as a rise in intracellular calcium and CD3-dependent cytotoxicity. These results should alert clinicians that CD3 resistant cytotoxic T cells can emerge during OKT3 therapy and may cause rejection. Immunotherapy that targets additional cell surface structures may be of benefit.

The importance of class I and class II HLA in cadaveric renal transplantation

The importance of avoiding mismatches (MM) at Class I and Class II HLA antigens in cyclosporine-treated renal allograft patients is controversial. In order to assess the role of HLA, 200 consecutive cadaveric renal allografts over a 4-year period were analysed. All patients received cyclosporine/predinisone immunosuppression and 75% were induced with ALG. Minimum follow-up period was one year. HLA A, B, DR, DQ, and DRw52/53 typing were available on 77-100% of allografts. A beneficial effect was noted at the HLA A locus. One-year survival was 87.2% in the 0 and 1 HLA A MM group combined vs 73.8% in the 2 HLA A MM group (p less than 0.05). The mean creatinine level at one year was also lower in the 0 plus 1 MM vs 2 MM group: 152.8 mumol/L vs 184.8 mumol/L, respectively (p less than 0.05). Significantly fewer rejection episodes occurred in the 0 and 1 HLA DQ MM group combined vs the 2 MM group. Steroid-resistant rejection episodes (SRRE) were not associated with the number of HLA MM. Patients who had an SRRE had significantly higher mean current and historical peak panel reactive antibodies (PRA) than patients who did not have SRRE. These results indicate that avoiding mismatches at the HLA A locus may improve renal allograft survival, and matching at HLA DQ may predispose patients to a more quiescent post-transplant course. The degree of preoperative sensitization may be an important etiologic factor in SRRE.

The therapy of rejection

Allograft rejection remains the single largest impediment to success in the field of organ transplantation. Advances in T cell physiology have resulted in refinement of the therapy of rejection. This article briefly reviews a few of the pathogenetic mechanisms underlying rejection and presents a simplified view of pharmacologic effects of the most commonly used agents (azathioprine, corticosteroids, cyclosporine, and polyclonal and monoclonal antibodies). As knowledge increases, it is hoped that one day the transplant physician will be able to specifically suppress the recipient against the donor's antigens, leaving the rest of the immune system intact to protect the host against infections.

In vitro IgM and IgM rheumatoid factor production in response to Staphylococcus aureus Cowan I and pokeweed mitogen: the contribution of CD5+ (Leu 1) B cells

The relation between the percentage of circulating CD5+ CD20+ B cells and the ability to synthesize IgM and IgM rheumatoid factor (RF) in vitro in response to pokeweed mitogen (PWM) and Staphylococcus aureus Cowan I (SAC) was assessed in 21 healthy controls. CD5+ CD20+ cells ranged from 7.3 to 19.9% of total CD20+ B cells. By Spearman's rank correlation, there was an inverse relation between the percentage of CD5+ CD20+ B cells and IgM production in response to PWM (rs = -0.452, p less than 0.05) and a direct correlation with RF production in response to SAC (rs = 0.450, P less than 0.05). The percentage of CD5+ CD20+ B cells was not related to any serologic HLA-A, B, C or D antigen. Healthy individuals may be predisposed to producing IgM or autoantibodies based on the percentage of circulating CD5+ Cd20+ B cells.

Role of class II HLA in cadaveric renal transplantation: a recent update

Class II HLA matching, especially HLA-DQ and DR, significantly improved allograft survival. HLA-DQ and DR matching may also be associated, in general, with a quiescent posttransplantation course, reduced incidence of SRRE, and somewhat better response to OKT3 rescue therapy. We conclude that the matching of class II HLA remains an important predictor of transplant outcome in CyA-treated patients and should form the primary basis of organ sharing.

Long-term patient and renal allograft survival in HBsAg infection: a recent update

Although the risk of HBsAg infection has now been reduced significantly by screening of blood, isolation of HBsAg+ patients, and more recently by vaccination, transplant-eligible patients can still be seen. We observed an increased mortality in HBsAg+ patients during 5 to 10 years posttransplantation. However, this could not be attributed to liver disease or dysfunction. Increased mortality and morbidity due to liver disease or dysfunction 10 years posttransplantation suggest that the HBsAg+ patients remain at a higher risk for developing liver disease during that period. In our study, HBsAg+ patients had a 10-year posttransplantation period relatively free of serious liver disease or dysfunction. Furthermore, both HBsAg+ and HBsAg- patients had a similar long-term allograft survival. It is unknown how the use of cyclosporine will affect those survival statistics. We, therefore, believe that HBsAg positivity per se should not constitute an absolute contraindication to transplantation.

Recurrence of acute rejection in the absence of CD3-positive lymphocytes

Allograft rejection is the single largest impediment to successful transplantation. Therapy targeted to lymphocytes has been in practice for many years using polyclonal heteroantisera. These products are generally accepted as being useful for the prevention and treatment of rejection; however, there have been problems with specificity, lot to lot variability, and supply. Therapy with monoclonal antibodies such as OKT3 may circumvent these problems and may allow for refined specificity. OKT3 has been shown to be highly effective at reversing acute renal allograft rejection. The few treatment failures were attributed to anti-mouse antibodies eliminating the OKT3, or to delay of therapy to such a late stage that rejection was irreversible. We present two cases which demonstrate successful reversal of acute rejection in cadaveric renal transplants by OKT3. The reversal was transient, however, in both cases, as both patients experienced recurrence of rejection while still receiving the monoclonal antibody. This occurred despite the absence of CD3-positive cells in the peripheral blood, and the presence of excess OKT3 in the serum. This implies that CD3-negative lymphocytes may under certain circumstances contribute to the rejection phenomenon.

Decreased expression of CD7 occurs in rheumatoid arthritis

To evaluate the possibility of antigenic modulation in vivo, we studied the expression of the CD7 antigen on the surface of peripheral blood and intrasynovial lymphocytes from patients with rheumatoid arthritis (RA). This disease is noted for features predicting changes in CD7: (1) increased expression related to activation during an immune response through possible contact with 'disease associated antigens' and (2) decreased expression associated with lymphocytes moving through tissue. We found a highly significant decrease of CD7 on RA T cells in vivo (P less than 10(-4] that was not related to disease activity, drug ingestion, or abnormalities in the ability of RA T cells to express or modulate the antigen in vitro. Similar decreased expression was observed on many intrasynovial T cells that were nevertheless activated as measured by expression of activation markers such as Act I (a late lymphocyte activation antigen) and Act II (the transferrin receptor). Decreased expression of CD7 occurs naturally in vivo in RA; this observation may have future significance in better understanding the immunopathogenesis of this disease.

Role of class I and class II HLA antigens in cadaveric renal transplantation

HLA matching at MT and DQ appears to be an important predictor of allograft survival. Allografts with no MM at MT and DQ have a good outcome while a known MM at MT and DQ appears to be associated with poor allograft outcome. Thus, our priority should be to avoid an MM for these broad-reacting specificities and then to minimize incompatibilities at DR and HLA-B. Furthermore, our data indicate that allografts with MM at DQ and two MMs at HLA-B appear to be at a higher risk. Perhaps these latter transplants should not be performed with conventional immunosuppressive therapy.

Two-color flow cytometry and functional analysis of lymphocytes cultured from human renal allografts: identification of a Leu-2+3+ subpopulation

The phenotype of T lymphocyte subsets present in renal biopsies showing acute cellular allograft rejection in six patients on cyclosporine have been characterized in situ by immunoperoxidase staining, and after expansion in vitro in interleukin 2 (IL-2) by two-color flow cytometry, sorting, and functional analysis. After 8 to 42 days in organ culture, both Leu-3+ (CD4) and Leu-2+ (CD8) subsets were found in each culture, in a ratio that varied from 0.2 to 5.0, which was not significantly different than the results of in situ immunoperoxidase staining of the uncultured biopsy. The cultured cells were almost all Leu-4+ (CD3) T cells (89% +/- 4), which expressed the activation markers DR (82% +/- 6) and the IL 2 (CD25) receptor (15% +/- 4). The Leu-3+ cells were largely Leu-8- (90% +/- 6), whereas a minority of the Leu-2+ cells were Leu-15+ (CD11) (26% +/- 4). Only a small fraction of the Leu-2+ cells stained for Leu-7 (8% +/- 6). Functional analysis of FACS-purified Leu-2-3+ and Leu-2+3- populations indicated that both subsets proliferated in response to graft donor antigens in a mixed lymphocyte reaction (MLR) and produced IL 2. Only the Leu-2+3- population demonstrated donor-specific cytotoxic activity. A minor subpopulation in each culture were both Leu-3+ and Leu-2+ (2.0%). Leu-2+3+ cells from one biopsy were purified to homogeneity (99.8%), and were found to express the T cell antigen receptor complex Ti/CD3 (WT-31+, Leu-4+), but not the common thymocyte antigen CD1 (OKT6). The Leu-2+3+ cells neither responded in the MLR, nor showed any cytotoxic capacity. The Leu-2+3+ cells were capable of IL 2 but not interferon-gamma production. None of the purified cultures demonstrated NK activity. A subset of the purified Leu-2+3+ cells lost Leu-2+ during 1 to 3 wk in culture, and became Leu-2-3+. These studies provide evidence that the cells that infiltrate renal allografts during rejection include alloproliferative, lymphokine-producing cells of both Leu-2+ and Leu-3+ subsets. The Leu-2+3- cells are also highly cytotoxic against donor lymphocytes, indicating the presence of helper independent cytotoxic T cells. A minor population of Leu-2+3+ T cells that do not express donor specific function was also identified.

Two-color flow cytometry and functional analysis of lymphocytes cultured from human renal allografts: identification of a Leu-2+3+ subpopulation

The phenotype of T lymphocyte subsets present in renal biopsies showing acute cellular allograft rejection in six patients on cyclosporine have been characterized in situ by immunoperoxidase staining, and after expansion in vitro in interleukin 2 (IL-2) by two-color flow cytometry, sorting, and functional analysis. After 8 to 42 days in organ culture, both Leu-3+ (CD4) and Leu-2+ (CD8) subsets were found in each culture, in a ratio that varied from 0.2 to 5.0, which was not significantly different than the results of in situ immunoperoxidase staining of the uncultured biopsy. The cultured cells were almost all Leu-4+ (CD3) T cells (89% +/- 4), which expressed the activation markers DR (82% +/- 6) and the IL 2 (CD25) receptor (15% +/- 4). The Leu-3+ cells were largely Leu-8- (90% +/- 6), whereas a minority of the Leu-2+ cells were Leu-15+ (CD11) (26% +/- 4). Only a small fraction of the Leu-2+ cells stained for Leu-7 (8% +/- 6). Functional analysis of FACS-purified Leu-2-3+ and Leu-2+3- populations indicated that both subsets proliferated in response to graft donor antigens in a mixed lymphocyte reaction (MLR) and produced IL 2. Only the Leu-2+3- population demonstrated donor-specific cytotoxic activity. A minor subpopulation in each culture were both Leu-3+ and Leu-2+ (2.0%). Leu-2+3+ cells from one biopsy were purified to homogeneity (99.8%), and were found to express the T cell antigen receptor complex Ti/CD3 (WT-31+, Leu-4+), but not the common thymocyte antigen CD1 (OKT6). The Leu-2+3+ cells neither responded in the MLR, nor showed any cytotoxic capacity. The Leu-2+3+ cells were capable of IL 2 but not interferon-gamma production. None of the purified cultures demonstrated NK activity. A subset of the purified Leu-2+3+ cells lost Leu-2+ during 1 to 3 wk in culture, and became Leu-2-3+. These studies provide evidence that the cells that infiltrate renal allografts during rejection include alloproliferative, lymphokine-producing cells of both Leu-2+ and Leu-3+ subsets. The Leu-2+3- cells are also highly cytotoxic against donor lymphocytes, indicating the presence of helper independent cytotoxic T cells. A minor population of Leu-2+3+ T cells that do not express donor specific function was also identified.

Characterization of in vivo-activated allospecific T lymphocytes propagated from human renal allograft biopsies undergoing rejection

To evaluate in situ lymphocyte responses in cell-mediated immune tissue injury, we have developed an approach for propagation of human allospecific T lymphocytes directly from tissue biopsies. We have utilized renal allograft tissue obtained from eight patients undergoing cellular rejection. Needle biopsy tissue was cultured in medium containing interleukin 2 (IL 2), including recombinant-DNA-produced IL 2. In each case, lymphoblasts migrated out of the tissue and increased in numbers, especially adjacent to the tissue. In two cases in which there was no cellular infiltrate present in the biopsy, no lymphocytes proliferated in vitro. Instead, fibroblasts eventually filled the wells from these allograft biopsies. The continued presence of the allograft tissue enhanced the viability and growth of the lymphoblasts in cultures from rejecting allografts. The isolated lymphoblasts had surface markers of mature OKT3+ lymphocytes of either OKT4+ or OKT8+ subsets. OKT8+ cells predominated. There was variability (41 to 97%) in the percentage of T lymphoblasts that bore surface HLA-DR antigens. In assays of lymphoblasts obtained from eight separate renal allografts, there was donor-specific cytotoxicity, and in all but two of the cases there was donor-induced proliferation. The specificity of the cytotoxic reaction was tested by using 51Cr-labeled, PHA-stimulated target cells prepared from a panel of HLA-typed donors. Proliferation was tested after 48 hr in the presence of mitomycin C-treated peripheral blood mononuclear cells as stimulator cells by using only 10(4) responder T lymphoblasts. Of particular note was that the cytotoxicity of the isolated lymphoblasts showed specificity against both "private" HLA class I alloantigens (of the allograft donor) as well as "public" cross-reacting epitopes. This method permits the propagation and functional characterization of in vivo-activated T lymphoblasts that are obtained from the actual sites of immune-mediated injury. Preliminary studies of other tissues with diverse inflammatory processes indicate the possible widespread applicability of obtaining in vivo-activated lymphocytes.

Characterization of in vivo-activated allospecific T lymphocytes propagated from human renal allograft biopsies undergoing rejection

To evaluate in situ lymphocyte responses in cell-mediated immune tissue injury, we have developed an approach for propagation of human allospecific T lymphocytes directly from tissue biopsies. We have utilized renal allograft tissue obtained from eight patients undergoing cellular rejection. Needle biopsy tissue was cultured in medium containing interleukin 2 (IL 2), including recombinant-DNA-produced IL 2. In each case, lymphoblasts migrated out of the tissue and increased in numbers, especially adjacent to the tissue. In two cases in which there was no cellular infiltrate present in the biopsy, no lymphocytes proliferated in vitro. Instead, fibroblasts eventually filled the wells from these allograft biopsies. The continued presence of the allograft tissue enhanced the viability and growth of the lymphoblasts in cultures from rejecting allografts. The isolated lymphoblasts had surface markers of mature OKT3+ lymphocytes of either OKT4+ or OKT8+ subsets. OKT8+ cells predominated. There was variability (41 to 97%) in the percentage of T lymphoblasts that bore surface HLA-DR antigens. In assays of lymphoblasts obtained from eight separate renal allografts, there was donor-specific cytotoxicity, and in all but two of the cases there was donor-induced proliferation. The specificity of the cytotoxic reaction was tested by using 51Cr-labeled, PHA-stimulated target cells prepared from a panel of HLA-typed donors. Proliferation was tested after 48 hr in the presence of mitomycin C-treated peripheral blood mononuclear cells as stimulator cells by using only 10(4) responder T lymphoblasts. Of particular note was that the cytotoxicity of the isolated lymphoblasts showed specificity against both "private" HLA class I alloantigens (of the allograft donor) as well as "public" cross-reacting epitopes. This method permits the propagation and functional characterization of in vivo-activated T lymphoblasts that are obtained from the actual sites of immune-mediated injury. Preliminary studies of other tissues with diverse inflammatory processes indicate the possible widespread applicability of obtaining in vivo-activated lymphocytes.

Lymphocyte activation antigens. I. A monoclonal antibody, anti-Act I, defines a new late lymphocyte activation antigen

Lymphocyte activation entails a sequence of events identified by analyzing the time course of expression of various distinctive cell surface molecules on lymphocytes that appear early (before initiation of DNA synthesis), parallel with DNA synthesis and cellular proliferation, or late (after peak proliferation). In this study we present identification of a novel late lymphocyte activation antigen, Act I, utilizing a murine monoclonal antibody. Anti-Act I was identified in a fusion of NS1 with BALB/c spleen cells immunized with a human tetanus toxoid-reactive T lymphoblast line. Flow cytometry analysis shows that Act I antigen is present in markedly greater amounts on activated T and B lymphocytes than on resting, small peripheral blood lymphocytes. Act I expression by these lymphocytes is promoted by PHA, tetanus toxoid, or alloantigens and lags behind maximal thymidine incorporation by 1 to 2 days. Thymocytes can be triggered to express Act I antigen during maturation induced by PHA/T cell growth factor stimulation. In vitro, anti-Act I does not affect antigen- or lectin-stimulated T cell proliferation, T cell-mediated lymphocytotoxicity, or T cell growth factor-induced proliferation of T lymphoblasts. By immunoperoxidase analysis, Act I antigen is restricted to lymphoid tissue, staining many lymphocytes in the paracortex, germinal centers, and mantle zones of lymph nodes, tonsil, and spleen. By immunoprecipitation, the Act I antigen is a single band of 63,000 m.w. on reduced or nonreduced SDS gels. The distribution, size, time course, and functional correlates indicate that Act I is different from other known T cell activation markers detected with anti-Tac, OKT9, B3/25, OKT10, 4F2, CBL1, and anti-Ia-like antibodies. Although the function of Act I is still undetermined, it may serve as a useful marker of a late stage of activation in vitro and in vivo.

Lymphocyte activation antigens. I. A monoclonal antibody, anti-Act I, defines a new late lymphocyte activation antigen

Lymphocyte activation entails a sequence of events identified by analyzing the time course of expression of various distinctive cell surface molecules on lymphocytes that appear early (before initiation of DNA synthesis), parallel with DNA synthesis and cellular proliferation, or late (after peak proliferation). In this study we present identification of a novel late lymphocyte activation antigen, Act I, utilizing a murine monoclonal antibody. Anti-Act I was identified in a fusion of NS1 with BALB/c spleen cells immunized with a human tetanus toxoid-reactive T lymphoblast line. Flow cytometry analysis shows that Act I antigen is present in markedly greater amounts on activated T and B lymphocytes than on resting, small peripheral blood lymphocytes. Act I expression by these lymphocytes is promoted by PHA, tetanus toxoid, or alloantigens and lags behind maximal thymidine incorporation by 1 to 2 days. Thymocytes can be triggered to express Act I antigen during maturation induced by PHA/T cell growth factor stimulation. In vitro, anti-Act I does not affect antigen- or lectin-stimulated T cell proliferation, T cell-mediated lymphocytotoxicity, or T cell growth factor-induced proliferation of T lymphoblasts. By immunoperoxidase analysis, Act I antigen is restricted to lymphoid tissue, staining many lymphocytes in the paracortex, germinal centers, and mantle zones of lymph nodes, tonsil, and spleen. By immunoprecipitation, the Act I antigen is a single band of 63,000 m.w. on reduced or nonreduced SDS gels. The distribution, size, time course, and functional correlates indicate that Act I is different from other known T cell activation markers detected with anti-Tac, OKT9, B3/25, OKT10, 4F2, CBL1, and anti-Ia-like antibodies. Although the function of Act I is still undetermined, it may serve as a useful marker of a late stage of activation in vitro and in vivo.