Using RNA Sequencing to Characterize the Tumor Microenvironment.

RNA sequencing (RNA-seq) is an integral tool in immunogenomics, allowing for interrogation of the transcriptome of a tumor and its microenvironment. Analytical methods to deconstruct the genomics data can then be applied to infer gene expression patterns associated with the presence of various immunocyte populations. High quality RNA-seq is possible from formalin-fixed, paraffin-embedded (FFPE), fresh-frozen, and fresh tissue, with a wide variety of sequencing library preparation methods, sequencing platforms, and downstream bioinformatics analyses currently available. Selection of an appropriate library preparation method is largely determined by tissue type, quality of RNA, and quantity of RNA. Downstream of sequencing, many analyses can be applied to the data, including differential gene expression analysis, immune gene signature analysis, gene pathway analysis, T/B-cell receptor inference, HLA inference, and viral transcript quantification. In this chapter, we will describe our workflow for RNA-seq from bulk tissue to evaluable data, including extraction of RNA, library preparation methods, sequencing of libraries, alignment and quality assurance of data, and initial downstream analyses of RNA-seq data to extract relevant immunogenomics features. Systems biology methods that draw additional insights by integrating these features are covered further in Chapters 28 - 30 .

Cardiopulmonary fitness in patients undergoing hematopoietic SCT: a pilot study.

Hematopoietic cell transplantation (HCT) is a life-saving treatment for patients with high-risk hematological malignancies. Prognostic measures to determine fitness for HCT are needed to inform decision-making and interventions. VO(2peak) is obtained by measuring gas exchange during cycle ergometry and has not been studied as a prognostic factor in HCT. Thirty-two autologous and allogeneic HCT patients underwent VO(2peak) and 6 Minute Walk (6MW) testing before HCT, and provided weekly symptom and health-related quality of life (HRQOL) assessments before HCT and concluding at Day 100. Twenty-nine patients completed pre-HCT testing. Pre-HCT VO(2peak) was positively correlated with pre-HCT 6MW (r=0.65, P<0.001) and negatively correlated with number of chemotherapy regimens and months of chemotherapy. Patients with lower VO(2peak) reported higher symptom burden and inferior HRQOL at baseline and during early post-HCT period. Patients with pre-HCT VO(2peak) <16 mL/kg/min had higher risk of mortality post HCT (entire cohort: hazard ratio (HR) 9.1 (1.75-47.0), P=0.01; allogeneic HCT patients only: HR 6.70 (1.29-34.75), P=0.02) and more hospitalized days before Day 100 (entire cohort: median 33 vs 19, P=0.003; allogeneic HCT patients only: median 33 vs 21, P=0.004). VO(2peak) pre-HCT is feasible and might predict symptom severity, HRQOL and mortality. Additional studies are warranted.

Effectiveness of etoposide chemomobilization in lymphoma patients undergoing auto-SCT.

The effectiveness of stem cell mobilization with G-CSF in lymphoma patients is suboptimal. We reviewed our institutional experience using chemomobilization with etoposide (VP-16; 375 mg/m(2) on days +1 and +2) and G-CSF (5 µg/kg twice daily from day +3 through the final day of collection) in 159 patients with lymphoma. This approach resulted in successful mobilization (>2 × 10(6) CD34+ cells collected) in 94% of patients (83% within 4 apheresis sessions). Fifty-seven percent of patients yielded at least 5 × 10(6) cells in 2 days and were defined as good mobilizers. The regimen was safe with a low rate of rehospitalization. Average costs were $14 923 for good mobilizers and $27 044 for poor mobilizers (P<0.05). Using our data, we performed a 'break-even' analysis that demonstrated that adding two doses of Plerixafor to predicted poor mobilizers at the time of first CD34+ cell count would achieve cost neutrality if the frequency of good mobilizers were to increase by 21%, while the frequency of good mobilizers would need to increase by 25% if three doses of Plerixafor were used. We conclude that chemomobilization with etoposide and G-CSF in patients with lymphoma is effective, with future opportunities for cost-neutral improvement using novel agents.

L-selectin is dispensable for T regulatory cell function postallogeneic bone marrow transplantation.

In murine models, the adoptive transfer of CD4(+) /CD25(+) regulatory T cells (T(regs) ) inhibited graft-versus-host disease (GvHD). Previous work has indicated a critical role for the adhesion molecule L-selectin (CD62L) in the function of T(regs) in preventing GvHD. Here we examined the capacity of naive wild-type (WT), CD62L(-/-) and ex vivo expanded CD62L(Lo) T(regs) to inhibit acute GvHD. Surprisingly, we found that CD62L(-/-) T(regs) were potent suppressors of GvHD, whereas CD62L(Lo) T(regs) were unable to inhibit disease despite being functionally competent to suppress allo T cell responses in vitro. Concomitant with improved outcomes, WT and CD62L(-/-) T(regs) significantly reduced liver pathology and systemic pro-inflammatory cytokine production, although CD62L(-/-) T(regs) were less effective in reducing lung pathology. While accumulation of CD62L(-/-) T(regs) in GvHD target organs was equivalent to WT T(regs) , CD62L(-/-) T(regs) did not migrate as well as WT T(regs) to peripheral lymph nodes (PLNs) over the first 2 weeks posttransplantation. This work demonstrated that CD62L was dispensable for T(reg) -mediated protection from GvHD.

Ex vivo inhibition of NF-kappaB signaling in alloreactive T-cells prevents graft-versus-host disease.

The ex vivo induction of alloantigen-specific hyporesponsiveness by costimulatory pathway blockade or exposure to immunoregulatory cytokines has been shown to inhibit proliferation, IL-2 production, and the graft-versus-host disease (GVHD) capacity of adoptively transferred T-cells. We hypothesized that inhibition of the intracellular NF-kappaB pathway in alloreactive T-cells, which is critical for T-cell activation events including IL-2 transcription, could lead to alloantigen hyporesponsiveness and loss of GVHD capacity. We demonstrate that treatment of mixed lymphocyte reaction (MLR) cultures with PS1145, a potent inhibitor of NF-kappaB activation, can induce T-cell hyporesponsiveness to alloantigen in primary and secondary responses while preserving in vitro responses to potent mitogenic stimulation. GVHD lethality in recipients of ex vivo PS1145-treated cells was profoundly inhibited. Parking of control or PS1145-treated MLR cells in syngeneic Rag(-/-) recipients resulted in intact contact hypersensitivity (CHS) responses. However, GVHD lethality capacity also was restored, suggesting that lymphopenic expansion uncoupled alloantigen hyporesponsiveness. These results indicate that the NF-kappaB pathway is a critical regulator of alloresponses and provide a novel small molecule inhibitor based approach that is effective in preventing early posttransplant GVHD lethality but that also permits donor T-cell responses to recover after a period of lymphopenic expansion.

Utility of obtaining blood cultures in febrile neutropenic patients undergoing bone marrow transplantation.

Infection remains an important cause of morbidity and mortality after bone marrow or stem cell transplantation. To evaluate the role of obtaining blood cultures for intermittent or persistent fever in neutropenic patients on antibiotic therapy, we performed a retrospective chart review of 196 consecutive patients admitted to the Bone Marrow Transplant Unit at the University of North Carolina Hospitals from 1995 to 1998. From the cohort of 196 patients, 154 patients developed neutropenic fever. The initial blood culture was positive in 16 of 145 patients during the first fever episode giving a prevalence of 11%. From the total of 109 patients that had blood cultures drawn after day 1 of fever, five patients had blood cultures positive for a pathogen, a prevalence of 4.6%. In only one patient, did blood cultures drawn after day 1 identify an organism not present on day 1 (prevalence 0.9%). After reviewing the results in the first 105 patients, we changed our timing of collection of blood cultures. Forty-nine patients were treated in this manner and we found that the mean number of blood cultures decreased from 9.2 to 4.7 per patient without a change in the frequency of infectious complications or length of hospitalization.

T-lymphocyte production of macrophage inflammatory protein-1alpha is critical to the recruitment of CD8(+) T cells to the liver, lung, and spleen during graft-versus-host disease.

To investigate the mechanism by which macrophage inflammatory protein-1alpha (MIP-1alpha) affects graft-versus-host disease (GVHD), the expression and function of MIP-1alpha in 2 murine models of GVHD were evaluated. In irradiated class I and class II disparate recipients, the expression of messenger RNA (mRNA) and protein for MIP-1alpha was significantly increased in GVHD target organs after transfer of allogeneic lymphocytes compared to syngeneic lymphocytes. When lymphocytes unable to make MIP-1alpha were transferred, there was a decrease in the production of MIP-1alpha in the liver, lung, and spleen of bm1 (B6.C-H2(bm1)/By) and bm12 (B6.C-H2(bm12)/KhEg) recipients compared to the transfer of wild-type splenocytes. At day 6 there was a 4-fold decrease in the number of transferred CD8(+) T cells in the lung and approximately a 2-fold decrease in the number of CD8(+) T cells in the liver and spleen in bm1 recipients after transfer of MIP-1alpha-deficient (MIP-1alpha(-/-)) splenocytes compared to wild-type (MIP-1alpha(+/+)) splenocytes. These differences persisted for 13 days after splenocyte transfer. In contrast, the number of donor CD4(+) T cells found in the liver and lung was significantly increased after the transfer of MIP-1alpha(-/-) compared to wild-type splenocytes in bm12 recipients from day 6 through day 10. Thus, the transfer of allogeneic T cells was associated with the enhanced expression of MIP-1alpha in both a class I and class II mismatch setting. However, the increased expression only led to enhanced recruitment of CD8(+), but not CD4(+), donor T cells. Production of MIP-1alpha by donor T cells is important in the occurrence of GVHD and functions in a tissue-dependent fashion.

Comparison of granulocyte colony-stimulating factor (G-CSF)--mobilized peripheral blood progenitor cells and G-CSF--stimulated bone marrow as a source of stem cells in HLA-matched sibling transplantation.

HLA-identical bone marrow or stem cell transplantation from a sibling is the preferred treatment for patients with chronic myelogenous leukemia, bone marrow failure syndromes, relapsed acute leukemia, and specific inborn errors of metabolism. Several groups have shown that granulocyte colony-stimulating factor (G-CSF)--mobilized peripheral blood progenitor cells (PBPCs) obtained from HLA-matched siblings are effective in reconstitution of marrow function after marrow ablative conditioning therapy. To evaluate whether G-CSF treatment before bone marrow harvest leads to enhanced recovery of PBPC counts and recovery from limited graft-versus-host disease (GVHD), we assessed the outcome of a sequential cohort of patients treated identically and then given either G-CSF--mobilized PBPCs or G-CSF--stimulated bone marrow from HLA-identical siblings. We show that the time to neutrophil engraftment is identical in the 2 cohorts, whereas platelet engraftment is earlier with the use of PBPCs. The incidence of acute GVHD was decreased, and that of chronic GVHD significantly decreased, in the group receiving bone marrow. Overall survival was not different between the 2 groups. Thus, G-CSF--stimulated bone marrow offers a source of stem cells that allows for early neutrophil engraftment with a decreased risk of GVHD.

T cell activity after dendritic cell vaccination is dependent on both the type of antigen and the mode of delivery.

Previous work in both human and animal models has shown that CTL responses can be generated against proteins derived from tumors using either peptide-pulsed dendritic cells (DCs) or nucleic acids from the tumor transfected into autologous DCs. Despite the efficacy of this approach for vaccine therapy, many questions remain regarding whether the route of administration, the frequency of administration, or the type of Ag is critical to generating T cell responses to these Ags. We have investigated methods to enhance CTL responses to a peptide derived from the human proto-oncogene HER-2/neu using mice containing a chimeric HLA A2 and H2Kb allele. Changes in amino acids in the anchor positions of the peptide enhanced the binding of the peptide to HLA-A2 in vitro, but did not enhance the immunogenicity of the peptide in vivo. In contrast, when autologous DCs presented peptides, significant CTL activity was induced with the altered, but not the wild-type, peptide. We found that the route of administration affected the anatomic site and the time to onset of CTL activity, but did not impact on the magnitude of the response. To our surprise, we observed that weekly administration of peptide-pulsed DCs led to diminishing CTL activity after 6 wk of treatment. This was not found in animals injected with DCs every 3 wk for six treatments or in animals initially given DCs weekly and then injected weekly with peptide-pulsed C1R-A2 transfectants.

CD8+ T cells are a biologically relevant source of macrophage inflammatory protein-1 alpha in vivo.

Chemokines are small proteins that direct the migration of leukocytes to inflammatory foci. Many cell types, including macrophages, fibroblasts, endothelial cells, and lymphocytes, produce chemokines in vitro, but biologically relevant sources of chemokines in vivo have not been well characterized. To investigate the pertinent sources of macrophage inflammatory protein-1 alpha (MIP-1 alpha) in vivo, we used MIP-1 alpha-deficient (MIP-1 alpha-/-) mice as donors and as recipients in adoptive transfer experiments after a lethal infection with Listeria monocytogenes (LM). Unexpectedly, we found that the production of MIP-1 alpha by CD8+ T cells was critical in this system, as the cells from MIP-1 alpha-/- mice primed with LM were significantly less effective in protecting naive mice against a lethal infection by LM than were the CD8+ T cells from wild-type (wt) mice. This requirement for donor T cell production of MIP-1 alpha was confirmed by the observation that wt donor T cells do not mediate protection when coadministered with an anti-MIP-1 alpha polyclonal antiserum. Production of MIP-1 alpha by the recipient mice was not required for protection, because wt and MIP-1 alpha-/- recipients were equally well protected by wt T cells. A 2- to 3-fold decrease in the number of transferred lymphocytes was seen in the spleens of mice receiving T cells from MIP-1 alpha-/- mice compared with those receiving wt T cells. In addition, CD8+ T cells from MIP-1 alpha-/- mice had a reduced ability to kill LM-infected target cells in vitro. These findings demonstrate that T cell production of MIP-1 alpha is required for clearance of an intracellular pathogen in vivo.

Murine T lymphocytes incapable of producing macrophage inhibitory protein-1 are impaired in causing graft-versus-host disease across a class I but not class II major histocompatibility complex barrier.

The routine use of bone marrow transplantation is limited by the occurrence of acute and chronic graft-versus-host disease (GVHD). Current approaches to decreasing the occurrence of GVHD after allogeneic transplantation use T-cell depletion, use immunosuppressive agents, or block costimulatory molecule function. The role of proteins in the recruitment of alloreactive lymphocytes has not been well characterized. Chemokines are a large family of proteins that mediate recruitment of mononuclear cells in vitro and in vivo. To investigate the role of T-cell production of the chemokine macrophage inhibitory protein-1 (MIP-1) in the occurrence of GVHD, splenocytes either from wild-type or from MIP-1-/- mice were administered to class I (B6.C-H2(bm1)) and class II disparate mice (B6-C-H2(bm12)). The incidence and severity of GVHD was markedly reduced in bm1 mice receiving splenocytes from MIP-1-/- mice as compared with mice receiving wild-type splenocytes. Bm1 mice receiving MIP-1-/- splenocytes had significantly less weight loss and markedly reduced inflammatory responses in the lung and liver than mice receiving C57BL/6 splenocytes. Bm1 mice receiving MIP-1-/- splenocytes had a markedly decreased production of antichromatin autoantibodies and impaired generation of bm1-specific T lymphocytes versus wild-type mice. However, MIP-1-/- splenocytes easily induced GVHD when administered to bm12 mice. This data show that blockade of chemokine production or function may provide a new approach to the prevention or treatment of GVHD but that chemokines that recruit both CD4(+) and CD8(+) lymphocytes may need to be targeted.

Prevention of infections in bone marrow transplant recipients.

Bone marrow transplantation (BMT) is increasingly used in the treatment of hematologic malignancies, solid tumors, and congenital diseases. The number of patients receiving a BMT increased from approximately 5000 in 1989 to 12,000 in 1995. Infectious complications are the most common cause of morbidity and mortality in the peritransplant period in patients undergoing autologous BMT. Additionally, infectious complications are a serious cause of complications in recipients of matched sibling allogeneic BMT, unrelated BMT, and related mismatched BMT.

A method for the production of CD4+ chronic myelogenous leukemia-specific allogeneic T lymphocytes.

The graft-versus-leukemia effect is critical to the maintenance of remission in patients transplanted for the treatment of chronic myelogenous leukemia (CML). A pivotal issue in transplantation for CML is whether donor lymphocytes are specific for host tumor or myeloid cells or a subset of the lymphocytes that cause graft-versus-host disease. We have enrolled seven patients in an experimental trial to evaluate the specificity of HLA-matched donor lymphocytes in vitro. We have produced 11 CD4+ cytotoxic and proliferative T-cell clones from five of the donors that only lyse or proliferate to leukemic myeloid cells. These T lymphocytes do not react with interleukin (IL)-2-stimulated blasts, natural killer-sensitive targets, donor neutrophils, or bcr-abl+ EBV-lymphoblastoid cell lines. We show that the addition of the cytokines IL-7 and IL-12 during the production of T-cell clones enhances the recovery of myeloid-specific clones in vitro. Five of the myeloid-specific clones that we produced maintained specificity over 12 weeks in culture. Adoption of this method should allow for the expansion and in vivo testing of CML-specific CD4+ T-cell clones in adoptive immunotherapy.

Long-term engraftment failure after marrow ablation and autologous hematopoietic reconstitution: differences between peripheral blood stem cell and bone marrow recipients.

We infused peripheral blood stem cells (PBSC) into 51 patients with various malignant disorders, after myeloablative conditioning. Twenty-four patients also received autologous bone marrow (PBSC + BM). In a multivariate analysis, the only statistically significant predictors of neutrophil engraftment were log-dose CFU-GM (P < 0.001) and the number of prior chemotherapy regimens (P = 0.004). The factors predicting RBC and platelet engraftment were log-dose CFU-GM (P = 0.002), PBSC + BM infusion (P = 0.007) and the absence of neoplastic bone marrow involvement (P = 0.009). Seven patients remained platelet and/or red cell transfusion-dependent for 100 days or more post-transplant after good neutrophil recovery. Six of these seven long-term engraftment failures, as well as five additional patients, received < 10(5) CFU-GM/kg. Of the 11 patients who received < 10(5) CFU-GM/kg (low-dose patients), seven were PBSC recipients, of whom six were long-term engraftment failures. In contrast, there were no long-term engraftment failures among the four low-dose autologous marrow recipients. This difference in long-term engraftment failure rate was significant (P = 0.015). The low-dose PBSC patients all had a diagnosis of lymphoma with bone marrow involvement. The low-dose PBSC + BM group was more heterogeneous, but no patient had malignant involvement of the marrow. The low-dose PBSC patients had also received significantly more prior chemotherapy regimens than the low-dose PBSC + BM patients and a significantly higher proportion received total body irradiation (TBI) as part of their conditioning regimen. We conclude that marrow damage resulting from a combination of neoplastic infiltration, chemotherapy and TBI may result not only in low PBSC yields but also in an impaired capacity of the marrow microenvironment to support transplanted stem cells.

CD4+ cytolytic effectors are inefficient in the clearance of Listeria monocytogenes.

Cytotoxic T lymphocytes (CTL) recognize and lyse target cells through the interaction of the T-cell receptor complex with the class I or class II major histocompatibility complex (MHC). The production of class I-restricted CTL has been shown to be critical to the elimination of specific pathogens including Listeria monocytogenes. However, the function of class II-restricted CTL in the clearance of intracellular pathogens is poorly understood. H-2b beta 2-microglobulin-deficient mice (beta 2M-/-) are not able to produce CD8+ CTL in response to infection with L. monocytogenes. We used this model to evaluate the efficacy of class II-restricted CTL, in the absence of a class I-restricted response, during a primary infection with L. monocytogenes. We demonstrate that, despite their effectiveness in adoptive transfer of protection, Listeria-specific CD4+ class II-restricted cytotoxic lymphocytes are ineffective in decreasing titres of L. monocytogenes in the spleen was found established infection. In beta 2M-/- mice, persistence of L. monocytogenes in the spleen was found preferentially in class II-negative cells. Surprisingly, class I-restricted CTL from C57BL/6 mice were capable of decreasing bacterial titres during an established infection even in the absence of detectable class I on the surface of cells from beta 2M-/- mice. These data strongly suggest that, in the absence of a class I-restricted response, pathogens that elicit a class II-restricted cytotoxic response may escape prompt eradication by the immune system.

The role of lactoferrin as an anti-inflammatory molecule.

The formation of hydroxyl radical via the iron catalyzed Haber-Weiss reaction has been implicated in phagocyte-mediated microbicidal activity and inflammatory tissue injury. The fact that neutrophils contain lactoferrin and mononuclear phagocytes have the capacity to acquire exogenous iron has suggested that iron bound to lactoferrin may influence the nature of free radical products generated by these cells. Over the years the iron-lactoferrin complex has been heralded as both a promoter and inhibitor of hydroxyl radical formation. This manuscript is intended to provide an overview of work performed to date related to this controversy and to present results of a number of preliminary studies which shed further light on the role of lactoferrin in inflammation.

Blastomycosis in transplant recipients: report of a case and review.

Fungi cause serious, often fatal infections in immunocompromised hosts. Recipients of solid organ and bone marrow transplants are predisposed to invasive fungal infections with Candida species, Aspergillus species, and Cryptococcus neoformans. In contrast, infections with Blastomyces dermatitidis have rarely been diagnosed in transplant recipients. We describe a patient who received an orthotopic heart transplant and developed recurrent disseminated blastomycosis. Other reported cases of blastomycosis in transplant recipients are summarized. Clinical presentation, treatment options, and morbidity associated with infections with B. dermatitidis in transplant patients are reviewed.

Interaction of lactoferrin and lipopolysaccharide (LPS): effects on the antioxidant property of lactoferrin and the ability of LPS to prime human neutrophils for enhanced superoxide formation.

Lactoferrin is a 77-kDa iron-binding protein to which a wide variety of divergent biologic functions have been ascribed. It has recently been reported that lactoferrin interacts with bacterial lipopolysaccharide (LPS) in such a fashion as to affect the binding of lactoferrin to myeloid cells. Two other potential interactions of LPS and lactoferrin were explored. Lactoferrin prevents hydroxyl radical formation by binding iron, even at low pH. Lactoferrin inhibited iron-catalyzed formation of hydroxyl radical in the presence of LPS at pH 7.4 and 4.5. Low concentrations of LPS can be used to "prime" neutrophils toward enhanced function, such as formation of stimulated superoxide anion. Lactoferrin inhibited LPS priming of neutrophils if LPS contamination of the protein (provided by commercial suppliers) was first reduced. Inhibition of LPS priming was observed whether apolactoferrin or iron-saturated lactoferrin was used. Similar inhibition of LPS priming was observed when neutrophils were incubated with other serum proteins (e.g., albumin, apotransferrin, or iron-saturated transferrin). These results show that LPS should not be expected to affect the free radical biology of lactoferrin, which is a crucial physiologic function of this protein. However, lactoferrin inhibits LPS priming, and this effect requires consideration in experimental models of inflammation.

Uptake of lactoferrin by mononuclear phagocytes inhibits their ability to form hydroxyl radical and protects them from membrane autoperoxidation.

Human mononuclear phagocytes do not contain the iron-binding protein lactoferrin that we have previously demonstrated inhibits the potential for human neutrophils to generate hydroxyl radical in the presence of an exogenous iron catalyst of the Haber-Weiss reaction. Previous work by other investigators has suggested that mononuclear phagocytes (monocytes and monocyte-derived macrophages (MDM] have the capacity to bind exogenous lactoferrin via lactoferrin-specific membrane surface receptors. Accordingly, we examined the possibility that uptake of iron-free (apo) lactoferrin by human mononuclear phagocytes could play a role in limiting the potential for generation of hydroxyl radical during the monocyte/MDM respiratory burst. When monocytes or MDM were incubated in the presence of apo-lactoferrin, cell-associated lactoferrin increased in proportion to the concentration of lactoferrin provided. Similar results were obtained with iron-loaded (diferric) milk lactoferrin. Consistent with the in vivo importance of these findings, we found that lactoferrin was intimately associated with human alveolar macrophages obtained by bronchoalveolar lavage. The fucose polymer fucoidan inhibited lactoferrin uptake whereas exogenous transferrin or MDM exposure to IFN-gamma was without effect. Scatchard binding analysis confirmed the presence of a lactoferrin-specific receptor with a calculated kDa of 3.56 x 10(-6) M and 3.4 x 10(7) binding sites per cell. Subcellular fractionation studies indicated that twofold more of the lactoferrin which became cell-associated over the 1-h incubation time could be found in the cytoplasmic fraction compared to the plasma membrane-containing fraction, consistent with previous evidence by others for internalization of lactoferrin by mononuclear phagocytes. When lactoferrin-loaded monocytes/MDM were incubated in lactoferrin-free media, evidence for release of lactoferrin was obtained by SDS-PAGE and immunoblot analysis, suggesting the presence of a recyclable pool of cell-associated lactoferrin. To assess the impact of lactoferrin loading on monocyte/MDM hydroxyl radical formation, lactoferrin-loaded phagocytes were stimulated with PMA in the presence of catalytic iron. Hydroxyl radical generation by lactoferrin-loaded cells was decreased to about 50% of control cells. Similarly, monocytes that had been lactoferrin-loaded demonstrated a 28% decrease in autooxidation of their membrane when stimulated in the presence of catalytic iron. These data suggest that lactoferrin binding may play an important role in maintaining optimal mononuclear phagocyte function and protecting adjacent tissue from untoward phagocyte-associated hydroxyl radical generation.