Immunological characterization of canine hematopoietic progenitor cells

Cross-reactivity of commercially available anti-human monoclonal antibodies with canine cytokines: establishment of a reliable panel to detect the functional profile of peripheral blood lymphocytes by intracytoplasmic staining

BACKGROUND

The process for obtaining monoclonal antibodies against a specific antigen is very laborious, involves sophisticated technologies and it is not available in most research laboratories. Considering that most cytokines remain partially conserved among species during evolution, the search for antibody cross-reactivity is an important strategy for immunological studies in veterinary medicine. In this context, the amino acid sequence from human and canine cytokines have demonstrated 49-96 % homology, suggesting high probability of cross-reactivity amongst monoclonal antibodies. For this, 17 commercially available anti-human monoclonal antibodies [IL-1α, IL-1β, IL-2, IL-4, IL-5, IL-6, IL-8 (#1, #2), IL-10, IL-12, IL-13, IL-17A, IFN-γ (#1, #2), TNF-α (#1, #2) and TGF-β], were evaluated in vitro for intracellular cytokine detection in a stimulated canine blood culture by flow cytometry and confocal microscopy. Lymphocytes from peripheral blood of healthy and two unhealthy dogs were analyzed.

RESULTS

Eleven anti-human mAbs [IL-1α, IL-4, IL-5, IL-6, IL-8 (#1, #2), IL-12, IL-17A, TNF-α (#1, #2) and TGF-β] cross-reacted against canine intracellular cytokines. The specificity of the assays was not affected after Fc-blocking. Three anti-human cytokine mAbs [IL-4, IL-8 (#2) and TGF-β] when evaluated by confocal microscopy also cross-reacted with intracellular canine cytokines. The identification of human mAbs that cross-reacted with canine cytokines may support their use as immunological biomarkers in veterinary medicine studies.

CONCLUSION

The identification of these 11 anti-human cytokine mAbs that cross-reacted with canine cytokines will be useful immunological biomarkers for pathological conditions by flow cytometry and fluorescence microscopy in dogs.

Characterization of CD34⁺ thymocytes in newborn dogs

Using two-color flow cytometry, we characterized CD34(+) cells in the newborn canine thymus. CD34(+) thymic cells comprised approximately 5% of cells recovered by thymus tissue teasing and both large and small thymocytes have been present in this population, the former being 7-12 times more frequent. All CD34(+) cells expressed the pan-leukocyte antigen CD45. The expression of CD44 profile on the large and small CD34(+) thymocytes differed: almost all large CD34(+) cells were CD44(+), while only 75% of small CD34(+) thymocytes co-expressed the CD44 antigen. We have previously described that CD172α is present on the surface of CD34(+) bone marrow cells in dogs. In the thymus, CD172α was expressed on 5-10% and less than 5% of large and small CD34(+) cells, respectively. Some CD34(+) thymocytes also co-expressed T-lineage-specific markers like CD3, CD4, CD8, TCR1 and TCR2. Their expression increased during the large-to-small thymocyte transition. Based on our findings we suggest that thymocyte progenitors enter their primary differentiation center as large CD34(+), CD44(+), CD45(+) and CD172α(+) cells. T-cell specific markers appear on their surface at early stages of differentiation. As the size of progenitors decreases with terminal primary differentiation, the CD34, CD44, and CD172α surface markers are down-regulated.

Reactivity of cross-reacting monoclonal antibodies with canine leukocytes, platelets and erythrocytes

A panel of 380 commercially available monoclonal antibodies (mAbs) against human CD molecules from various sources was tested during the 8th Human Leukocyte Differentiation Antigen Workshop (HLDA8) for cross-reactivity on canine peripheral blood leukocytes by flow cytometry. In addition, all mAbs were used to label a 50:50 mixture of platelets and erythrocytes of the same dogs. This testing resulted in 51 cross-reacting mAbs. mAbs with specificity for CD9, CD29, CD42a, CD61, and CD41/CD61 showed cross-reactivity with canine platelets in a non-polymorphic and one mAb with the erythrocyte antigen CD235a in a polymorphic reaction pattern. Canine leukocyte-reactive mAbs included those with specificity for CD11a, CD11b, CD14, CD18, CD21, CD22, CD47, CD49d, CD49e, CD56, CD62L, CD91, CD94, and CD172a. In addition, several mAbs resulted in a staining pattern of canine cells which suggest that the canine epitope equivalents have an alternate expression pattern from that expected for humans (CD1a, CD35, CD44, CD45, CD75s, CD81). In summary, this study confirmed the reactivity of previously described cross-reactive mAbs with canine cells and resulted in the characterization of mAbs recognizing so far undetectable canine CD molecules.

Flow cytometric analysis of bone marrow leukocytes in neonatal dogs

Dogs represent both an important veterinary species and a convenient model for allogeneic hematopoietic stem cell transplantation. Even though anti-canine CD34 antibodies have recently become available, little is known about hematopoietic lineages in dogs, partially because CD34- cells have been ignored in all analyses performed so far. In this study, we have focused on the bone marrow mononuclear compartment to provide an additional piece of information on the phenotype of CD34+ progenitors and to identify the dominant CD34- population. We have shown that, in contrast to the adults, mature lymphocytes are scarce in neonatal dog bone marrow. Using cross-reactive antibodies against CD79alpha we have shown that the B lineage of hematopoiesis strongly prevails. CD34+ cells were shown to be positive for MHC class II and SWC3, a member of the signal regulatory protein family.

Evaluation of monoclonal antibodies for identification of subpopulations of myeloid cells in bone marrow obtained from dogs

OBJECTIVE

To evaluate monoclonal antibodies that may be useful for immunophenotyping myeloid cells in bone marrow of dogs.

SAMPLE POPULATION

Bone marrow specimens obtained from 5 dogs.

DESIGN

Specimens were labeled with monoclonal antibodies that detected CD18, major histocompatability antigen class-II (MHC class-II), CD14, and Thy-1. Cells labeled with each of the antibodies were isolated by use of a fluorescence-activated cell sorter. Differential cell counts of sorted cells were used to determine cells that were labeled by each of the various antibodies.

RESULTS

Myeloid cells labeled with anti-CD18 antibody included granulocytes, lymphocytes, and monocytes-macrophages. Immature and mature granulocytes were labeled. Lymphocytes, monocytes-macrophages, and eosinophils were labeled with anti-Thy-1 antibody. Cells labeled with anti-MHC-class II antibody included approximately 9% of bone marrow cells, which consisted almost exclusively of lymphocytes and monocytes-macrophages. Approximately 4% of bone marrow cells were labeled with anti-CD14 antibody, with > 90% of sorted cells being monocytes-macrophages.

CONCLUSIONS AND CLINICAL RELEVANCE

Four monoclonal antibodies for use in detecting subpopulations of canine bone marrow cells were evaluated. These antibodies should be useful in differentiating the origin of leukemic cells in dogs.

Studies on canine bone marrow long-term culture: effect of stem cell factor

Long-term culture of canine marrow cells allows in vitro studies of the hematopoietic system of the dog and characterization of early progenitor cells. Colonies of fresh marrow cells grew equally good in both agar or methylcellulose supplemented with fetal calf serum, while colonies of long-term cultures required agar-based medium containing human serum. Optimum colony growth was obtained when stem cell factor (SCF) and granulocyte-macrophage-colony-stimulating factor (GM-CSF) were used as growth stimuli of colony forming units (CFU). Similar results were achieved with several cell culture media. Addition of hydrocortisone to long-term cultures improved clonogenic growth of cultured cells. Addition of 2-mercaptoethanol had no effect. Strong differences were observed in long-term culture with different horse serum lots and the addition of fetal calf serum to long-term culture suppressed CFU growth of cultured cells. Recharging of cultures with fresh marrow cells on day 7 of culture improved CFU growth only in the following week but had little effect on the outcome. Adding SCF to long-term cultures led to differentiation of more primitive cells and destruction of the stromal layer. Investigation of purified and cultured cell populations was possible when preestablished long-term cultures as stromal layers were used. Loss of long-term culture-initiating ability could be demonstrated in this system with lineage negative marrow cells expanded ex vivo with SCF and GM-CSF.

Crossreactivity of workshop monoclonal antibodies with canine blood leukocytes

A selection of 164 monoclonal antibodies for determinants on porcine cells were tested on canine leukocytes by flow cytometry. Eighteen mAbs proved to be crossreacting and 16 of these reacted uniformly with cells of three unrelated dogs while two displayed a polymorphic reaction pattern.

Immune phenotype of canine hematopoietic progenitor cells

The immune phenotype of canine hematopoietic progenitor cells was studied by immunoseparation and culturing of separated cells. Two separation methods were used, the magnetic cell sorting system (MACS) and the fluorescence activated cell sorter (FACS). For separation rat anti dog antibodies Dog 13 and Dog 14 directed against Thy-1, and Dog 26 as well as cross-reactive mouse anti human antibodies IOT2a and 7.2 directed against MHC class II were used. Separated cell populations were cultured in semisolid agar before and after long-term culture on a pre-established irradiated stromal cell layer. After 28 days, adherent and nonadherent cells were harvested from long-term culture. The MACS system allowed separation of cells into positive and negative fractions. Long-term culture-initiating cells (LTC-IC) were found in both the Thy-1+ and the Thy-1- fraction, but the content of LTC-IC was higher in the Thy-1+ fraction. The MACS system did not allow separation of progenitor cells according to the expression of MHC class II antigen detected by Dog 26 and the cross-reactive antibodies IOT2a and 7.2. In contrast to the MACS system the FACS allowed separation of negative, low-positive and high-positive cell populations. Low-positive fractions were well defined for Thy-1 and less well defined for MHC class II. CFU before and after long-term culture were exclusively observed in the low positive fraction (Thy-1(lo+)). Using MHC class II antibody Dog 26 LTC-IC were found mainly in the negative and low positive fraction, and CFU were observed mainly in the low and high positive fraction. In conclusion pluripotent canine hematopoietic precursor cells are low positive for Thy-1 and for MHC class II. In this respect canine hematopoietic progenitor cells are comparable to those of mouse and man.

Reactivity of workshop antibodies with a non-ruminant species: crossreactivity with canine blood leukocytes

Three-hundred and eight monoclonal antibodies detecting surface determinants on ruminant cells were tested on canine leukocytes by flow cytometry. Thirty mabs showed crossreactivity: 25 of them reacted uniformly with cells of three unrelated dogs, five displayed a polymorphic reaction pattern. Thus, in addition to mabs with yet unknown specificity, antibodies to ruminant WC9, B-cell antigens and possible CD29, CD49d cross-react with canine cells, and probably react with the homologous canine antigen.