Activation of lymphocytes after platelet allotransfusion possessing only class I MHC product

A novel immunosuppressive pathway involving peroxynitrite-mediated [corrected] nitration of platelet antigens within antigen-presenting cells

BACKGROUND

Studies have demonstrated that immunity against platelet (PLT) transfusions is dependent on recipient antigen-presenting cells (APCs) and their ability to produce nitric oxide (NO). To further analyze this, we focused on NO's major metabolite peroxynitrite (ONOO(-)) and its ability to affect PLT immunity.

STUDY DESIGN AND METHODS

To address how NO and its major metabolite may mediate PLT immunity, GP91(PHOX) knockout (KO) mice that lack the ability to produce the ONOO(-) were transfused weekly with allogeneic BALB/c PLTs, and donor antibody development was analyzed.

RESULTS

Compared with controls, GP91(PHOX) KO mice developed significantly (p < 0.0001) higher-titered immunoglobulin G (IgG) donor antibodies by two transfusions, and this immune response could be inhibited by treating the recipient mice with aminoguanidine, a relatively selective inhibitor of inducible nitric oxide synthase. In vitro nitration of PLTs did not alter PLT antibody binding but significantly inhibited the transfused PLT's ability to stimulate IgG immunity in either wild-type or KO mice. The lack of nitrated PLT immunity correlated with an inability of APCs to mediate phagocytosis of nitrated PLTs. The lack of nitrated PLT immunity could only be restored when normal PLTs were mixed with the nitrated PLTs and transfused.

CONCLUSION

The results identify a dual role for NO metabolism within APCs that significantly modulates PLT immunity; nitration of PLT antigens leads to lack of immunity due to an inability of APCs to move PLT antigens intracellularly whereas there exists an NO-dependent pathway that stimulates anti-PLT immunity.

The pattern of cytokine gene expression in human colorectal carcinoma

Systemic and local cytokine environment may modulate the immunogenicity of colorectal cancer cells, and affect anti-tumor immune functions of tumor-infiltrating lymphocytes. We therefore investigated cytokine mRNA expression patterns in tumors and peripheral blood mononuclear cells (PBMC) from patients with colorectal adenocarcinoma. IL-2, IFN-gamma, tumor necrosis factor-alpha (TNF-alpha), IL-4, IL-6, IL-8, IL-10 and IL-1 beta mRNAs in single cell suspension of freshly isolated colorectal cancer tissue were studied by RT-PCR. Frequencies of cytokine gene expression were compared to those in normal colonic mucosa from tumor patients. The frequencies of IL-2, IFN-gamma, IL-4 and IL-10 gene expression were also determined in peripheral blood mononuclear cells from patients with colorectal adenocarcinoma and compared to those of healthy individuals. Tumor samples were more frequently positive for IFN-gamma, IL-2, TNF-alpha and IL-10 gene expression than normal mucosa (p=0.0001, p=0.0118, p=0.001 and p<0.0001, respectively). Frequencies of IL-2 and TNF-alpha gene expressions were significantly higher in tumors with a diameter <5 cm, than in those with a diameter >5 cm. The genes for IL-6, IL-1 beta and IL-8 were commonly expressed in both tumor tissue and normal colonic mucosa. IFN-gamma transcripts were detected in more PBMC samples from patients with colorectal cancer than those from normal controls (p=0.0449). Thus, colorectal cancer tissue is characterized by a specific pattern of cytokine gene expression. It is likely that multiple interactions between pro- and anti-inflammatory cytokines regulate tumor growth and the functional activity of tumor-infiltrating lymphocytes.

Extreme Leukoreduction of Major Histocompatibility Complex Class II Positive B Cells Enhances Allogeneic Platelet Immunity

In a murine model of platelet alloimmunization, we examined the definitive role that mononuclear cells (MC) have in modulating platelet immunity by using platelets from severe combined immunodeficient (SCID) mice. CB.17 (H-2d) SCID or BALB/c (H-2d) mouse platelets were transfused weekly into fully allogeneic CBA (H-2k) mice and antidonor antibodies measured by flow cytometry. MC levels in BALB/c platelets were 1.1 ± 0.6/μL and SCID mouse platelets could be prepared to have significantly lower (<0.05/μL) MC numbers. Transfusions with 108 BALB/c platelets (containing ≈100 MC/transfusion) stimulated IgG antidonor antibodies in 100% of the recipients by the fifth transfusion, whereas 108 SCID mouse platelets (containing ≈5 MC/transfusion) stimulated higher-titered IgG alloantibodies by the second transfusion. When titrations of BALB/c peripheral blood MC were added to the SCID mouse platelets, levels approaching 1 MC/μL reduced SCID platelet immunity to levels similar to BALB/c platelets. Characterization of the alloantibodies showed that the low levels of MC significantly influenced the isotype of the antidonor IgG; the presence of 1 MC/μL was associated with induction of noncomplement fixing IgG1 antidonor antibodies, whereas platelet transfusions, devoid of MC (<0.05/μL), were responsible for complement-fixing IgG2a production. When magnetically sorted defined subpopulations of MC were added to the SCID platelets, major histocompatability complex (MHC) class II positive populations, particularly B cells, were found to be primarily responsible for the reduced SCID mouse platelet immunity. The presence of low numbers of MC within the platelets was also associated with an age-dependent reduction in platelet immunogenicity; this relationship however, was not observed with SCID mouse platelets devoid of MC. The results suggest that a residual number of MHC class II positive B cells within allogeneic platelets are required for maximally reducing alloimmunization.

Extreme Leukoreduction of Major Histocompatibility Complex Class II Positive B Cells Enhances Allogeneic Platelet Immunity

In a murine model of platelet alloimmunization, we examined the definitive role that mononuclear cells (MC) have in modulating platelet immunity by using platelets from severe combined immunodeficient (SCID) mice. CB.17 (H-2d) SCID or BALB/c (H-2d) mouse platelets were transfused weekly into fully allogeneic CBA (H-2k) mice and antidonor antibodies measured by flow cytometry. MC levels in BALB/c platelets were 1.1 ± 0.6/μL and SCID mouse platelets could be prepared to have significantly lower (&lt;0.05/μL) MC numbers. Transfusions with 108 BALB/c platelets (containing ≈100 MC/transfusion) stimulated IgG antidonor antibodies in 100% of the recipients by the fifth transfusion, whereas 108 SCID mouse platelets (containing ≈5 MC/transfusion) stimulated higher-titered IgG alloantibodies by the second transfusion. When titrations of BALB/c peripheral blood MC were added to the SCID mouse platelets, levels approaching 1 MC/μL reduced SCID platelet immunity to levels similar to BALB/c platelets. Characterization of the alloantibodies showed that the low levels of MC significantly influenced the isotype of the antidonor IgG; the presence of 1 MC/μL was associated with induction of noncomplement fixing IgG1 antidonor antibodies, whereas platelet transfusions, devoid of MC (&lt;0.05/μL), were responsible for complement-fixing IgG2a production. When magnetically sorted defined subpopulations of MC were added to the SCID platelets, major histocompatability complex (MHC) class II positive populations, particularly B cells, were found to be primarily responsible for the reduced SCID mouse platelet immunity. The presence of low numbers of MC within the platelets was also associated with an age-dependent reduction in platelet immunogenicity; this relationship however, was not observed with SCID mouse platelets devoid of MC. The results suggest that a residual number of MHC class II positive B cells within allogeneic platelets are required for maximally reducing alloimmunization.

Evidence for the continuous recruitment and activation of T cells into the joints of patients with rheumatoid arthritis

Rheumatoid arthritis (RA) synovial fluid (SF) T cells express the activation markers CD69, HLA-DR and very late antigen (VLA)-1, but surprisingly few bear interleukin-2 receptors (CD25). This unusual activation state is commonly assumed to be due to stimulation by local antigen, yet T cells activated in vitro express activation antigens in the clearly defined sequence: CD69, CD25, HLA-DR and finally VLA-1. Two possible explanations for the activation state of SF cells are: first, they comprise several subpopulations each expressing different activation antigens or, second, activation markers are up-regulated by mechanisms other than antigen stimulation. To examine these hypotheses, double- and triple-color immunofluorescence techniques were applied to four T cell populations: normal peripheral blood T cells activated in vitro, RA SF T cells, T cells from an in vivo model of migration [tuberculin purified protein derivative (PPD)-induced skin blisters] and T cells co-cultured with endothelial cells (EC). The results confirmed that in vitro activated T cells expressed activation markers in the sequence described above, with significant CD25 expression and few cells co-expressing CD69 with HLA-DR or VLA-1. In contrast, almost half the SF T cells were CD69+HLA-DR+ but CD25-; a significant minority were CD69+VLA-1+. T cells from PPD-induced skin blisters were already HLA-DR+ and VLA-1+ at 24 h, although, in vitro, PPD-activated T cells up-regulated HLA-DR and VLA-1 only after 1 week, suggesting that pre-activated T cells were preferentially recruited into the blisters. Finally, T cells were found to up-regulate CD69 and, to a lesser extent, HLA-DR after adhering to EC in vitro. In summary, the paradoxical activation state of SF T cells cannot be explained solely by single or multiple rounds of activation in situ. At least two other mechanisms, the preferential recruitment of pre-activated T cells and the induction of HLA-DR and especially CD69 by endothelial contact during migration, may also play a role.

Clinical applications of phenotypic analysis

The ability to track lymphocyte differentiation and activation via the expression of cell surface marker molecules has had an enormous impact on diagnosis, monitoring and therapy of a wide range of diseases. Here, Katalin Pálóczi highlights studies from Hungary on the clinical applications of such analysis.