The induction of suppressor T cells by concanavalin A is independent of cellular proliferation and protein synthesis

The effects of PEG-interleukin-2 and interleukin-2 on essential hypertension and cellular immune function in the spontaneously hypertensive rat

The effects of recombinant human interleukin-2 covalently linked to polyethylene glycol (PEG-IL-2) or interleukin-2 (IL-2) on hypertension and in vitro suppressor T cell function in the spontaneously hypertensive rats (SHR) were investigated. Male young prehypertensive (4 weeks old) SHRs and adult (10 weeks old) SHRs with established hypertension were injected with low (5,000 units (u)/kg) or high (50,000-100,000 u/kg) dose of PEG-IL-2 or IL-2 as a single bolus or repeated injections. Systolic blood pressure was measured twice weekly using the tail-cuff technique. Systolic blood pressure in the PEG-IL-2 or IL-2 treated animals, irrespective of age, dose, or route of injection, did not differ significantly from that measured in vehicle-treated controls over a 10 week period. Mean arterial pressure measured by intra-arterial catheter was 159 +/- 7 mm Hg 10 weeks after treatment with repeated injections of 5,000 u/kg of PEG-IL-2 and 158 +/- 9 mm Hg in vehicle-treated controls. All rats injected with IL-2 had IL-2-specific IgG antibody in their sera. None of the PEG-IL-2 treated rats had any detectable anti-IL-2 antibodies in their sera. Thus, PEG-IL-2 showed far less immunogenicity than IL-2. Suppressor T (Ts) cells generated from adult SHR spleen cells failed to suppress pokeweed mitogen (PWM)-driven immunoglobulin G (IgG) synthesis. PEG-IL-2 or IL-2 supplementation both in vitro and in vivo restored the ability of adult SHR to generate Ts cells able to inhibit IgG synthesis. Our data suggest that PEG-IL-2 or IL-2 administration does correct a prominent defective Ts cell activity found in adult SHR, but that correction of this immune abnormality is not attended by an attenuation of hypertension.

Abnormal T suppressor cell function in juvenile rheumatoid arthritis

The purpose of this study was to analyze T suppressor cell function in juvenile rheumatoid arthritis (JRA). JRA is a chronic inflammatory childhood disease of unknown etiology that is characterized by arthritis and immunoregulatory abnormalities. T suppressor cell precursors (CD8+, CD28-) were purified from the peripheral blood of 24 JRA patients, using a combination of monoclonal antibodies. These cells were treated with histamine or concanavalin A, agents that are known to induce suppressor activity. They were also tested for their ability to inhibit the proliferative response of autologous T cells to phytohemagglutinin. In some experiments, the accumulation of intracellular cAMP following histamine treatment was also measured. Twelve of 13 patients with clinically active JRA showed abnormal histamine-inducible T suppressor cell function, characterized by the failure of CD8+, CD28- T cells to mediate any detectable suppression. The failure of these cells to accumulate intracellular cAMP after histamine treatment was observed in 5 of 5 patients tested who had active disease. In contrast, 11 of 11 patients with clinically inactive JRA, 5 of 5 patients with cystic fibrosis, and 9 of 9 pediatric control subjects had normal histamine- and concanavalin A-inducible T suppressor cell function, and a normal cAMP response to histamine. These results suggest that patients with clinically active JRA have a reversible defect in T suppressor cell function that is associated with a failure of T suppressor cell precursors to accumulate intracellular cAMP following their exposure to selected immune stimuli.

Allocation of the suppressive activity of normal peripheral blood lymphocytes induced by diffusion chamber culture and Con A stimulation to the G2 phase of the cell cycle

Peripheral blood mononuclear cells stimulated either by diffusion chamber culture or by a high Con A concentration exhibit suppressive activity under conditions where no increase in cell number takes place. Instead an accumulation of large cells is observed which, according to their DNA contents, are classified as cells in the G2 phase of the cell cycle. By elutriation separation the suppressive activity is shown to be confined to this cell cycle phase.

Antigen-specific suppression of anti-influenza antibody production in man. Possible role of a membrane-antigen complex

E rosette-forming (E+) cells from human secondary lymphoid tissue were incubated with high dose influenza A virus (Mem-Bel) in an attempt to generate suppressor T cells. Suppression was assayed by transferring the antigen-pulsed E+ cells into effector cultures consisting of E+ and E- cells stimulated with immunogenic amounts of either the inducing virus Mem-Bel) or the non-cross-reacting influenza B virus (B/HK). The transfer resulted in marked inhibition of IgG, IgA and IgM antibody production to Mem-Bel but not to the control antigen, B/HK virus. The suppressive effect was specific at the level of induction as well as expression since E+ cells exposed to high dose Mem-Bel could provide help to an effector culture containing E- cells and optimal dose of B/HK virus. However, metabolically active cells did not appear to be required for suppression. Thus, it could be elicited (a) after only 15 min incubation of E+ cells with high-dose virus and (b) by E+ cells exposed to irradiation, incubated in the presence of metabolic inhibitors, or disrupted by repeated freeze thawing. In contrast, treatment of E+ cells with pronase reversed the suppressive effect. Interestingly, virus heated to 70 degree C failed to induced suppression, while retailing the ability to elicit a normal helper response. Suppression induced by exposure to standard amounts of high-dose antigen was mediated by T cells of both helper/inducer (Leu-3a+) and suppressor/cytotoxic subsets (Leu-2a+), but not by B cells. Two groups of observations pointed to the B cell as the target of suppression. First, suppression could still be transferred to effector cultures in which helper T cells had been replaced by T cell-replacing factor or suppressor T cells removed by irradiation. Second, significant inhibition of antibody production was obtained when the transfer of antigen-pulsed E+ cells was delayed for up to 120 h after initiation of the effector culture. Taken together the results suggest that suppression in this system is due to the formation of an antigen bridge between specific receptor sites on the T cell membrane and the target. Although not dependent on triggering of metabolically active suppressor T cells the phenomenon highlights the need for care in interpreting the mechanism of suppression by high-dose antigen and could, in addition, represent a biologically important control mechanism capable of rapid inhibition of effector T cells and B cells in sites of high antigen concentration.

Replication variants of the human inactive X chromosome. II. Frequency and replication rate relative to the other chromosomes of the complement

Replication variants of the inactive X chromosome were investigated in lymphocytes from six donors by means of terminal BrdU or thymidine incorporation. There were interindividual differences in the incidence of particular variants. In endoreduplicated and tetraploid cells both allocyclic X chromosomes showed the same replication sequence. The Xp22 band of the allocyclic X chromosome seemed to replicate later than the homologous material in some cells. Initiation time of DNA synthesis within the inactive X chromosome was found to be stable; termination time, however, varied greatly relative to the other chromosomes. Early completion of replication within the heterochromatic X chromosome could be demonstrated preferentially for the Xq25-27 terminal sequence, but other variants expressed the phenomenon also. A variable replication rate of the inactive X chromosome is believed to be responsible for its asynchronous, independent replication. The biological significance of the phenomenon is discussed with respect to cell differentiation.

The effect of azathioprine on terminal differentiation of human B lymphocytes

The effect of azathioprine on the terminal differentiation of human B cells triggered in vitro by pokeweed mitogen and S. aureus Cowan I bacteria was studied. AZ caused an enhancement of Ig synthesis in its lower concentrations, a phenomenon dependent on the inactivation of suppressor T cells. Higher drug concentrations impaired T-helper function as well as B cell differentiation of peripheral blood, lymph node, and spleen lymphocytes.

Modulation of human T lymphocyte functions by isoprinosine

Isoprinosine was shown to alter certain T cell functions. In vitro, it has previously been shown to induce suppressor cell activity in both mouse and human lymphocytes. Our in vitro results suggest that Isoprinosine acts on immune balance by increasing the number of non-suppressor T cells and, at least partially blocks Con A induced suppressor activity. In vitro NK activity remained unaltered.

Concanavalin A reduces liver collagen accumulation in murine schistosomiasis

Mice infected with Schistosoma mansoni develop hepatic fibrosis associated with enhanced collagen synthesis that out-paces induced collagenase activity. Administration of one dose of concanavalin A [Con A (200 micrograms)] by i.p. injection to mice at 5 or 6 weeks after infection with 50 S. mansoni cercariae decreased liver collagen content by 50% compared to levels in control-infected mice injected with either homologous immunoglobulin (200 micrograms) or phosphate-buffered saline; additional doses of Con A had no further effect. The decrease in collagen content could not be attributed to either decreased egg deposition in the liver or inhibition of liver collagen synthesis, but was coincident with a greater solubility of granulomas. Collagen contents of skin and tail were unaffected. The relative solubilities of liver collagen in 8 M urea: 10 mM dithiothreitol were greater in treated animals as compared to controls. However, the amounts of collagen solubilized were similar in both sets of animals, since the total collagen content of treated mice was 50% of the controls. A possible explanation for these results is that much of the synthesized collagen does not accumulate in treated animals, whereas it does accumulate in controls. Peak collagenase and neutral protease activities occurred at 7 weeks postinfection in treated animals, and were 2-fold greater than in controls. Similar effects were observed when succinylated Con A was administered. The results suggest that Con A may modulate host-immune responses influencing fibrogenesis in hepatic murine schistosomiasis.

Concanavalin A-induced alteration of surface marker expression on murine T cells

The activation of suppressor T cells by Concanavalin A (Con A) was characterized by changes in expression of T cell surface markers. Treatment of normal mouse spleen cells with monoclonal antibody to Ly-1 prior to activation with Con A consistently reduced the resulting suppressor cell activity as assayed by mixed culture with primed spleen cells responding to sheep erythrocytes. Addition of indomethacin to anti-Ly-1 depleted spleen cells together with Con A had no effect on the resulting suppressor cell activity, whereas its addition to normal spleen cells together with Con A significantly abrogated suppressor T cell induction. In contrast, treatment of normal spleen cells with anti-Ly-1 following 24h culture with Con A had no effect on resulting suppressor cell activity. Treatment of spleen cells either prior to or following culture with Con A with monoclonal antibody to Ly-2 completely abrogated suppressor T cell activity. Suppressor T cells activated by Con A were depleted significantly by fractionation on columns containing insolubilized histamine. In contrast, fractionation of normal spleen cells on histamine columns followed by culture with Con A had no effect on subsequent suppressor T cell induction. Furthermore, direct addition of histamine (5 x 10(-4) M - 5 x 10(-8) M) to Con A preculture had no effect on resultant suppressor T cell generation, suggesting that possible immunodulatory actions of histamine may be expressed at the effector rather than during induction stages of Con A-induced suppressor T cell activation.