LFA—1／ICAM—1单抗对ConA诱导脾淋巴细胞增殖及分…

通过研究ＬＦＡ－１／ＩＣＡＭ－１单抗对Ｃｏｎ Ａ诱导的脾淋巴细胞活化增殖及其分泌细胞因子的影响，探讨了ＬＦＡ－１／ＩＣＡＭ－１分子在Ｔ细胞活化过程中所起的共刺激作用。结果表明，单独应用ＬＦＡ－１α链单抗（Ｍ１７／４．４．１１．９）或ＩＣＡＭ－１单抗（ＹＮ１／１．７．４）均不能引起脾淋巴细胞的增殖，但在加入ＣｏｎＡ诱导脾淋巴细胞增殖反应的最初８小时内加入ＬＦＡ－１单抗可以剂量依赖性地抑制ＣｏｎＡ诱导     

B7／CD28和ICAM—1／LFA—1共刺激信号对T及B细胞功？…

目的 研究共刺激途径Ｂ７／ＣＤ２８和ＩＣＡＭ－１／ＬＦＡ－１对Ｔ细胞活化以及Ｂ细胞效应的作用。方法 在体外建立ＡＰＣ：Ｔ：Ｂ细胞反应系统,用Ｂ７－１单抗和ＩＣＡＭ－１单抗分别阻断Ｂ７／ＣＤ２８和ＩＣＡＭ－１／ＬＦＡ－１共刺激途径,利用＾３Ｈ－ＴｄＲ法检测Ｔ细胞增殖,ＥＬＩＳＡ法测定Ｂ细胞分泌的杭体,用ＲＴ－ＰＣＲ法检测细胞因子基因的表达。结果 Ｂ７－１单抗和ＩＣＡＭ－１单坑均可抑制Ｔ细胞增殖及ＩＬ     

B7/CD28和ICAM-1/LFA-1共刺激信号对T及B细胞功能影响的研究

目的　研究共刺激途径Ｂ７／ＣＤ２８ 和ＩＣＡＭ１／ＬＦＡ１ 对Ｔ 细胞活化以及Ｂ 细胞效应的作用。方法　在体外建立ＡＰＣＴＢ 细胞反应系统, 用Ｂ７１ 单抗和ＩＣＡＭ１ 单抗分别阻断Ｂ７／ＣＤ２８ 和ＩＣＡＭ１／ＬＦＡ１ 共刺激途径, 利用３ ＨＴｄＲ 法检测Ｔ 细胞增殖,ＥＬＩＳＡ 法测定Ｂ 细胞分泌的抗体, 用ＲＴＰＣＲ 法检测细胞因子基因的表达。结果　Ｂ７１ 单抗和ＩＣＡＭ１ 单抗均可抑制Ｔ 细胞增殖及ＩＬ２ 的产生。Ｂ７１ 单抗可下调Ｂ 细胞抗体的产生（ Ｐ＜ ０ ．０５） , 而ＩＣＡＭ１ 单抗未见明显的抑制（ Ｐ＞ ０ ．０５） 。Ｂ７１ 单抗和ＣｓＡ 联用能阻断Ｔ 细胞增殖活性及Ｂ 细胞的效应, 而ＩＣＡＭ１ 单抗和ＣｓＡ联用则无此作用。Ｂ７１ 单抗能下调ＩＬ２ 和ＩＦＮγｍ ＲＮＡ 表达,Ｂ７１ 单抗和ＣｓＡ 联用则阻断ＩＬ２ 和ＩＦＮγｍ ＲＮＡ 表达,ＩＬ４ 和ＩＬ１０ ｍ ＲＮＡ 仍可表达。结论　Ｂ７／ＣＤ２８ 和ＩＣＡＭ１／ＬＦＡ１ 共刺激途径在Ｔ 细胞活化中具有不同的作用,Ｂ７１ 单抗和ＣｓＡ 联用可导致Ｔ 细胞功能失活即无能。     

粘附分子对CD3介导的胸腺细胞[Ca^2＋]i应答的影响

ＬＦＡ－１和ＩＣＡＭ－１广泛表达于各胸腺细胞亚群，但ＩＣＡＭ－１在ＰＮＡ￣＋细胞的表达下调。本文报道：用抗ＬＦＡ－１／ＩＣＡＭ－１和抗ＣＤ３单抗，分析了粘附分子ＬＦＡ－１／ＩＣＡＭ－１对抗ＣＤ３诱导的胸腺细胞［Ｃａ￣（２＋）］ｉ应答的影响。结果显示，可溶性抗ＬＦＡ－１／ＩＣＡＭ－１可抑制ＣｏｎＡ刺激的胸腺细胞增殖，且以抗ＬＦＡ－１抗体的作用更为显著，在ＣｏｎＡ或抗ＣＤ３诱导的胸腺细胞［Ｃａ￣（２＋）］ｉ应答中，抗ＬＦＡ－１单抗可明显抑制［Ｃａ￣（２＋）ｉ升高。但如果用二抗交联ＣＤ３和ＬＦＡ－１，胸腺细胞［Ｃａ￣（２＋）ｉ则显著高于单独交联ＣＤ３时的水平（Ｐ＜０．０１），而ＣＤ３与ＩＣＡＭ－ｌ交联却无此效应，此外，仅交联ＬＦＡ－１或ＩＣＡＭ－１也无诱导［Ｃａ￣（２＋）］ｉ应答的作用。提示在ＬＦＡ－ｌ与ＩＣＡＭ－１介导的胸腺细胞与胸腺基质细胞相互作用中，ＬＦＡ－１可为ＴＣＲ／ＣＤ３途径介导的胸腺细胞活化提供复合刺激信号。     

胸腺基质细胞单抗Pf18－3诱导LFA－1依赖的胸腺细胞粘附聚集

试验发现大鼠抗小鼠胸腺基质细胞单抗Ｐｆ１８－３与新鲜胸腺细胞共育可诱发明显的细胞粘附聚集发生。细胞聚集约出现于共育１０小时，约２４小时细胞聚集达高峰，聚集率为６８％。其达高峰时间比ＰＭＡ诱发同样细胞聚集约晚８小时，但两者诱发细胞聚集的时间过程基本相同（ＰＭＡ主要通过ＬＦＡ－１／ＩＣＡＭ－１途径诱发细胞粘附）。在无二价离子（Ｃａ＋＋、Ｍｇ＋＋）或有ＥＤＴＡ存在的培基中及４℃的条件下Ｐｆ１８－３不能诱发细胞聚集，这与整合素家族粘附因子作用特征相似。抗ＬＦＡ－１、ＩＣＡＭ－１的单抗具有明显的不同程度抑制Ｐｆ１８－３单抗或ＰＭＡ诱发的细胞聚集，抑制率分别为：Ｐｆ１８－３７４％及４３％；ＰＭＡ６２％及３６％。在固相抗ＣＤ３的单抗诱导胸腺细胞增殖试验中，Ｐｆ１８－３单抗同样诱发细胞聚集，但明显抑制ＣＤ３单抗诱导的胸腺细胞增殖，抑制率为５７．７％。实验结果提示ＬＦＡ－１／ＩＣＡＭ－１参与了Ｐｆ１８－３单抗诱导的新鲜胸腺细胞粘附聚集，其效应为抑制细胞增殖。     

抗Thy—1单克隆抗体的免疫抑制作用

从体内，体外研究了抗Ｔｈｙ－１单克隆抗体（Ｍｃ－Ａｂ）的免疫抑制作用，结果表明：（１）体外抗Ｔｈｙ－１ＭｃＡｂ在补体参与下能够杀伤小鼠胸腺细胞，无补体时能抑制ＣｏｎＡ诱导的Ｔ淋巴细胞增殖反应；（２）在体内，可以抑制小鼠脾细胞对ＣｏｎＡ和ＰＨＡ诱导的Ｔ淋巴细胞增殖，但不影响ＬＰＳ诱导的Ｂ淋巴细胞增殖反应。结果说明：抗Ｔｈｙ－１ＭｃＡｂ的免疫抑制使用可能包括补体依赖性细胞毒作用和通过Ｔｈｙ－１分子 地     

抗Thy－1单克隆抗体的免疫抑制作用

从体内、体外研究了抗Ｔｈｙ－１单克隆抗体（ＭｃＡｂ）的免疫抑制作用。结果表明：（１）体外抗Ｔｈｙ－１ＭｃＡｂ在补体参与下能够杀伤小鼠胸腺细胞，无补体时能抑制ＣｏｎＡ诱导的Ｔ淋巴细胞增殖反应；（２）在体内，可以抑制小鼠脾细胞对ＣｏｎＡ和ＰＨＡ诱导的Ｔ淋巴细胞增殖、但不影响ＬＰＳ诱导的Ｂ淋巴细胞增殖反应。结果说明：抗Ｔｈｙ－１ＭｃＡｂ的免疫抑制作用可能包括补体依赖性细胞毒作用和通过Ｔｈｙ－１分子对Ｔ淋巴细胞功能的抑制。     

LFA—1／ICAM—1与T细胞发育

粘附分子ＬＦＡ－１／ＩＣＡＭ－１是发育期Ｔ细胞和胸腺基质细胞（ＴＳＣ）表重面要的膜分子之一，不同Ｔ细胞亚群和不同部位或类型的ＴＳＣ表面表达的水平各异，ＬＦＡ－１与配基ＩＣＡＭ－１的结合在介导Ｔ细胞与Ｔ细胞、Ｔ细胞与ＴＳＣ之间的相互作用（辅助信号传导）以及胸腺细胞克隆选择等过程中发挥重要作用。     

LFA－1／ICAM－1与T细胞发育

粘附分子ＬＦＡ－１／ＩＣＡＭ－１是发育期Ｔ细胞和胸腺基质细胞（ＴＳＣ）表重面要的膜分子之一，不同Ｔ细胞亚群和不同部位或类型的ＴＳＣ表面表达的水平各异，ＬＦＡ－１与配基ＩＣＡＭ－１的结合在介导Ｔ细胞与Ｔ细胞、Ｔ细胞与ＴＳＣ之间的相互作用（辅助信号传导）以及胸腺细胞克隆选择等过程中发挥重要作用。     

LFA-1/ICAM-1在柯萨奇B组病毒播散感染中的作用初探

目的观察ＣｏｘＢ３感染大鼠单个核细胞，诱导细胞表面ＬＦＡ－１表达的变化，以及ＬＦＡ－１／ＩＣＡＭ－１在ＣｏｘＢ３从单个核细胞向心肌细胞播散感染中的作用。方法制备和培养大鼠心肌细胞和大鼠外周血单个核细胞，并进行病毒感染；制备和纯化分泌抗大鼠ＬＦＡ－１（ＣＤ１１ａ）和抗大鼠ＩＣＡＭ－１（ＣＤ５４）的单克隆抗体；在Ｗｉｓｈ细胞上进行病毒感染性滴定，并观察细胞病变；流式细胞仪分析各组单个核细胞ＬＦＡ－１的表达情况；观察抗－ＬＦＡ－１和抗－ＩＣＡＭ－１单克隆抗体在ＣｏｘＢ３复制和播散感染中的作用。结果ＣｏｘＢ３感染大鼠外周血单个核细胞１８～２４小时可以诱导细胞膜ＬＦＡ－１表达增多，同时释放感染性病毒颗粒感染正常大鼠心肌细胞；加入抗－ＬＦＡ－１或抗－ＩＣＡＭ－１的单克隆抗体均可不同程度地抑制病毒向心肌细胞播散感染，并显著降低培养上清液中病毒滴度。结论ＣｏｘＢ３感染增加白细胞表面ＬＦＡ－１表达可能是病毒病理作用的重要步骤     

ICAM-1/LFA-1 interactions in T-lymphocyte activation and adhesion to cells of the blood-retina barrier in the rat.

To identify the signals involved in the adhesion and subsequent migration of lymphocytes across the endothelium (REC) and pigment epithelium (RPE) of the blood-retina barrier we have studied the effects of monoclonal antibodies (mAb) to rat adhesion/accessory molecules on the binding of normal and concanavalin A (Con A)-activated rat spleen lymphocytes to cultured unstimulated and interferon-gamma (IFN-gamma)-stimulated RPE and REC. Forty to 48% of unactivated T cells were found to bind to normal REC or RPE by leucocyte function-associated antigen-1/intercellular adhesion molecule-1 (LFA-1/ICAM-1)-independent mechanisms, despite constitutive expression of ICAM-1 by the RPE cells and LFA-1 by the T cells. Con A-activated lymphocytes showed an enhanced adhesion to both RPE and REC. However, IFN-gamma-stimulated RPE and REC did not demonstrate a significant increase in adhesiveness for normal lymphocytes highlighting the importance of lymphocyte integrin activation from low-affinity to high-affinity state. Activated lymphocyte adhesion to unstimulated RPE and REC was significantly blocked by LFA-1 mAb (35%, P < 0.0001) and ICAM-1 mAb (20%, P < 0.001). Inhibition of adhesion by antibody to CD2 was not significant. Both ICAM-1 and LFA-1 mAb also significantly (P < 0.05) blocked antigen presentation following retinal extract stimulation of lymphocytes from immunized rats in proliferation assay. These data suggest that the ICAM-1/LFA-1 system is important in lymphocyte trafficking into the eye only after lymphocyte activation.     

Accessory cell function of a human colonic epithelial cell line HT-29 for bacterial superantigens

The expression and up-regulation of cell adhesion molecules on a human colonic epithelial cell line HT-29, and the peripheral blood T lymphocyte proliferation responses to bacterial superantigens presented by this cell line were investigated, compared with peripheral blood monocytes. In HT-29 cells, there was constitutive expression of intercellular adhesion molecule-1 (ICAM-1) and lymphocyte function-associated antigen-3 (LFA-3) at a low level, but no constitutive expression of HLA-DR, LFA-1, B7-1 and B7-2 molecules. After stimulation with the supernatants of staphylococcal enterotoxin B (SEB)-stimulated peripheral blood mononuclear cells for 48 h, there was significant up-regulation of HLA-DR and ICAM-1 molecules (both >90% positive). However, this stimulation had no effect on the expression of LFA-1, B7-1, B7-2 and LFA-3 molecules. In the presence of all tested superantigens SEB, toxic shock syndrome toxin-1, and streptococcal pyogenic exotoxin A, stimulated HT-29 cells caused significant T cell proliferation. When monocytes were used as antigen-presenting cells (APC), the MoAbs against HLA-DR, B7-2 and LFA-3 showed a significant inhibition of SEB-induced T cell proliferation. Anti-ICAM-1 MoAb had no effect on this response. On the other hand, when stimulated HT-29 cells were used as APC, the MoAbs against HLA-DR and ICAM-1 significantly inhibited SEB-induced T cell proliferation. In contrast to monocytes, anti-B7-2 and anti-LFA-3 had no effect on this response. SEB could not induce HT-29 cells to produce IL-8 directly; however, SEB significantly induced the stimulated HT-29 cells to produce IL-8 in the presence of T cells. Thus these data demonstrate that the products of superantigen-stimulated T cell activation can increase the expression of HLA-DR and ICAM-1 molecules on HT-29 cells significantly. Stimulated HT-29 cells can serve as APC to bacterial superantigens. This response is an HLA-DR- and ICAM-1-dependent, but B7-2- and LFA-3-independent process, which was different from professional APC monocytes.     

Interleukin 4 induces cellular adhesion among B lymphocytes

We here report that interleukin 4 (IL-4) alone is able to induce cellular adhesion among mouse lymphocytes, and together with lipopolysaccharide (LPS), it increases the adhesion induced by LPS. The adhesion was inhibited by antibodies against IL-4. IL-4 appears to be acting mainly on B lymphocytes, since the response caused by IL-4 alone was much less sensitive to depletion of adherent cells than the LPS response. Depletion of T cells had no effect on IL-4- or LPS-induced adhesion. IL-4 could together with Con A, but not alone, induce adhesion among T cells. Cell clusters, which were formed after 2-3 days of LPS plus IL-4 stimulation, could be completely dissociated, and when the cells were recultured in medium, they readily started to reaggregate. The adhesion molecule lymphocyte function-associated antigen 1 (LFA-1) is, at least in part, involved in LPS plus IL-4-induced adhesion. Antibodies against LFA-1 inhibited the adhesion, but antibodies against other cell surface molecules were without inhibitory effect. Adhesion induced by IL-4 alone may involve other adhesion molecules than LFA-1.     

Interleukin 4 Induces Cellular Adhesion Among B Lymphocytes

Abstract

We here report that interleukin 4 (IL-4) alone is able to induce cellular adhesion among mouse lymphocytes, and together with lipopolysaccharide (LPS), it increases the adhesion induced by LPS. The adhesion was inhibited by antibodies against IL-4. IL-4 appears to be acting mainly on B lymphocytes, since the response caused by IL-4 alone was much less sensitive to depletion of adherent cells than the LPS response. Depletion of T cells had no effect on IL-4- or LPS-induced adhesion. IL-4 could together with Con A, but not alone, induce adhesion among T cells. Cell clusters, which were formed after 2-3 days of LPS plus IL-4 stimulation, could be completely dissociated, and when the cells were recultured in medium, they readily started to reaggregate. The adhesion molecule lymphocyte function-associated antigen 1 (LFA-1) is, at least in part, involved in LPS plus IL-4-induced adhesion. Antibodies against LFA-1 inhibited the adhesion, but antibodies against other cell surface molecules were without inhibitory effect. Adhesion induced by IL-4 alone may involve other adhesion molecules than LFA-1.     

Co-stimulation of T cells results in distinct IL-10 and TNF-alpha cytokine profiles dependent on binding to ICAM-1, ICAM-2 or ICAM-3.

The LFA-1 adhesion molecule is involved in cell adhesion events of leukocytes through binding to ICAM-1, ICAM-2 and ICAM-3. Whether binding to either of these ligands similarly affects co-stimulation of T cells and cytokine secretion is unknown. We demonstrated that LFA-1 co-stimulation under suboptimal concentrations of anti-CD3 monoclonal antibodies resulted in high, intermediate and weak proliferation of T cells on ICAM-1, -2, and -3, respectively, which correlates with the distinct affinities of LFA-1 for these ligands. Furthermore, we investigated whether binding to ICAM-1, -2 or -3 induced different cytokine profiles, thus regulating T helper cell function. Granulocyte-macrophage colony-stimulating factor and IFN-gamma were secreted in high amounts, whereas IL-2, IL-4 and IL-5 could not be detected. Interestingly, we observed that LFA-1/ICAM-1 co-stimulation of T cells resulted in high production of the Th2 cytokine IL-10 compared to ICAM-2 or ICAM-3 co-stimulation. In contrast, ICAM-2 and ICAM-3 induced a much stronger secretion of the Th1 cytokine TNF-alpha compared to LFA-1/ICAM-1 induced co-stimulation, despite the lower proliferation rate. These results demonstrate that besides facilitating cell adhesion, LFA-1 serves as a potent co-stimulatory molecule by inducing different cytokine patterns depending on the ligand bound.     

T-lymphocyte responsiveness in murine schistosomiasis mansoni is dependent upon the adhesion molecules intercellular adhesion molecule-1, lymphocyte function-associated antigen-1, and very late antigen-4.

Granuloma formation in murine schistosomiasis is dependent on CD4+ Th lymphocytes and requires recruitment and accumulation of inflammatory cells at the site of egg deposition. The present study examined the role of three adhesion molecules, intercellular adhesion molecule-1 (ICAM-1), lymphocyte function-associated antigen-1 (LFA-1), and very late antigen-4 (VLA-4), that participate in cellular recruitment, interaction, and lymphocyte activation during in vitro activation of acutely and chronically infected spleen and liver granuloma lymphocytes. Blockade of ICAM-1, LFA-1, or VLA-4 by rat monoclonal antibody inhibited spleen and granuloma lymphocyte interleukin-2 (IL-2) and IL-4 production as well as lymphoproliferative responses at similar levels (66 to 87%). The down-modulated cytokine and proliferative responses of chronically infected lymphocytes were inhibited to the same extent as their acutely infected counterparts. Cell sorting analysis demonstrated that acutely and chronically infected splenic and granuloma lymphocytes expressed similar levels of LFA-1, ICAM-1, and VLA-4 and that more ICAM-1 was expressed on infected than on uninfected mouse lymphocytes. By exposure of cells to paired monoclonal antibodies at suboptimal doses, it was determined that whereas all three adhesion molecules may participate, only ICAM-1 and LFA-1 showed synergistic interactions in determining lymphocyte responsiveness. These data suggest that spleen and liver granuloma lymphocytes are equally well armed with functional adhesion receptors. Thus, ICAM-1, LFA-1, and VLA-4 play an important accessory role in inflammatory cytokine production and lymphocyte proliferation, and therefore these adhesion molecules may participate in the initiation and maintenance of the granulomatous inflammation.     

IL-12 plays a pivotal role in LFA-1-mediated T cell adhesiveness by up-regulation of CCR5 expression

The chemokine receptor CCR5 has been implicated in the recruitment of T cells to inflammatory sites. However, the regulation of CCR5 induction on T cells and its contribution to T cell adhesiveness are poorly understood. Using a Th1 clone, 2D6, that can be maintained with interleukin (IL)-12 or IL-2 alone (designated 2D6(IL-12) or 2D6(IL-2), respectively), we investigated how CCR5 is induced on T cells and whether CCR5 is responsible for up-regulating the function of adhesion molecules. 2D6(IL-12) grew, forming cell aggregates, in culture containing IL-12. This was due to lymphocyte function-associated antigen (LFA)-1-intercellular adhesion molecule (ICAM)-1 interaction, because 2D6(IL-12) expressed both LFA-1 and ICAM-1 and cell aggregation was inhibited by anti-ICAM-1 monoclonal antibody. Despite comparable levels of LFA-1 and ICAM-1 expression, 2D6(IL-2) cells did not aggregate in culture with IL-2. It is important that there was a critical difference in CCR5 expression between 2D6(IL-12) and 2D6(IL-2); the former expressed high levels of CCR5, and the latter expressed only marginal levels. Both types of cells expressed detectable albeit low levels of RANTES (regulated on activation, normal T expressed and secreted) mRNA. Unlike IL-12 or IL-2, IL-18 induced high levels of RANTES mRNA expression without modulating CCR5 expression. Therefore, combined stimulation with IL-12 and IL-18 strikingly up-regulated 2D6 cell aggregation. Notably, LFA-1-mediated aggregation of 2D6(IL-12) cells was suppressed by anti-CCR5 antibody. These results indicate that IL-12 plays a critical role in CCR5 expression on Th1 cells and consequently contributes to CCR5-mediated activation of LFA-1 molecules.     

Characterization of tissue outgrowth developed in vitro in patients with rheumatoid arthritis: involvement of T cells in the development of tissue outgrowth

BACKGROUND: The aim of this study was to analyze cellular and cytokine interactions governing the development of synovial tissue outgrowth in patients with rheumatoid arthritis (RA). METHODS: A single-cell suspension of dissociated synovial tissues of RA patients was cultured for a long period to develop tissue outgrowth. The resulting tissue outgrowth was characterized by immunohistochemical staining and ELISA. RESULTS: The tissue outgrowth developed in vitro included various cell types, such as macrophage-like synovial cells, fibroblast-like synovial cells and lymphocytes. Even after prolonged cultivation, synovial cells devoid of infiltrating T lymphocytes did not form tissue outgrowth. The outgrowth contained CD3+ cells, LeuM3 (CD14)+ cells and HLA-DR+ cells. The T cells expressed lymphocyte function-associated antigen (LFA)-1 and CD2, and the synovial cells expressed intracellular adhesion molecule (ICAM)-1 and LFA-3, suggesting possible interactions via LFA-1/ICAM-1 and CD2/LFA-3. Production of T-cell derived IFN-gamma and IL-17 and synovial-cell-derived fibroblast growth factor (FGF)-1 and IL-15 was confirmed in the tissue outgrowth as well as in RA synovial tissue. These cell types stimulate each other by secreting cytokines, leading to the secretion of proinflammatory cytokines and matrix metalloproteinase (MMP)-1 by the tissue outgrowth and proliferation of both lymphocytes and synovial cells. CONCLUSION: This study emphasizes the importance of cellular interactions between T cells and synovial cells, via adhesion molecules and the secretion of cytokines with stimulatory activity towards other cell types, for the hyperactivity of RA synovial cells.     

Role of LFA-1/ICAM-1 in interleukin-2-stimulated lymphocyte proliferation

Major adhesion routes between lymphoid cells involve the receptor/ligand pairs LFA-l/ICAM-1 and CD2/LFA-3, in addition to VLA or CD44 molecules. In this study we evaluated the role of these adhesion receptors in the proliferative response of lymphoid cells to interleukin-2 (IL-2). Blocking studies were performed with a panel of monoclonal antibodies (mAb) directed against these adhesion molecules. Selective inhibition of recombinant (r)IL-2-induced cell proliferation was observed with mAb directed against the a or /3 subunit of LFA-1 or to its ligand ICAM-1. Interestingly, rIL-2-induced proliferation was also inhibited by NKI-L16, an anti-la antibody known to enhance cell-cell interaction. Resting lymphocytes were preferentially susceptible to the inhibition, particularly in an early phase of culture and when stimulated with a relatively low dose of rIL-2. By using mAb that specifically could block distinct rIL-2 activation pathways, LFA-l/ICAM-1 interaction was found to be required for p55 IL-2 receptor (IL-2R)-mediated interaction of rIL-2 with its high-affinity receptor, but not for p75 IL-2R-mediated responses. Furthermore, it was shown that the rIL-2 response of T lymphocytes, but not of natural killer cells, was dependent on LFA-l/ICAM-1 interaction. This suggests that LFA-l/ICAM-1 interaction is required for an optimal rIL-2 response of cells capable of IL-2 secretion. Our data provide evidence for the hypothesis that adhesion receptor-directed release of IL-2 may result in a locally high concentration of IL-2 that triggers high-affinity IL-2R signaling and up-regulates p55 IL-2R to enhance cytokine responsiveness.