ABSTRACT
Natural killer (NK) cells play a crucial role in regulating immune functions. Few studies have characterized canine NK cells. We previously demonstrated that canine peripheral blood lymphocytes (PBLs) with a low surface CD5 density (CD5lo) are considered a critical NK population. Natural killer cells in most mammals do not express T-cell markers, but canine CD5lo cells express surface molecules, such as CD3 T-cell receptors. These features make canines unique models for the study of comparative immunology in NK cells. In this study, we discovered that CD5lo and CD21 double-negative (CD5lo-ne/CD2-) cells were originally low in NK cytotoxicity and their NK cytotoxicity was highly activated when co-cultured with CD5lo NK cells. The cytotoxicity was not activated when co-cultured with other cell types, such as high surface CD5 density (CD5hi) cells. The CD5lo-negative (CD5lo-ne) population comprises CD5- and CD5hi cells. CD5-cells were low in NK cytotoxicity initially or after culturing with interleukin-2 (IL-2) without CD5lo cells; however, the addition of CD5lo cells in a similar medium markedly enhanced the NK activity. By contrast, CD5hi cells were always NK inactive, irrespective of them being cultured with CD5lo cells or not. We further verified that only the CD5-CD21- cells, which were separated from CD5-CD21+ cells in the entire CD5- population, showed activated NK activity through CD5lo cell induction. This study is the first to reveal that canine NK cells enhanced NK-inert cells to become NK-cytotoxic cells. Additionally, it is concluded that in beagles, except for CD5lo cells, CD5-CD21- cells show NK activity.
ABSTRACT
SDS-PAGE, Western blot analysis and immunohistochemical staining were used to detect heat shock proteins (HSPs) 60, 70 and 90 in canine transmissible venereal tumor (CTVT). Tissues tested for HSPs included: (1) tissues from different growth phases of CTVT tumors artificially induced in dogs; (2) tissues from other canine tumors; (3) normal dog tissues. Our results indicate that HSP 60 was consistently higher in CTVT cells in regressing phase than those in progressing phase. However, no detectable antibody response specific to the tested HSPs was found in the sera from CTVT-laden dogs in different growth phases. Although levels of the HSPs were all detectable in CTVT cells, only 60 and 70 were higher in CTVT cells than in normal tissues. In addition, none of the HSPs were detected in cells from five other canine tumors. These data suggest that canine HSP 60 and 70 are potential markers for CTVT and HSP 60 is appear to be involved in CTVT regression.PCR was used to confirm the existence of CTVT cells using primers designed to cover the sequence between the 5' end of c-myc near the first exon and the 3' end outside the LINE gene. Only CTVT samples were positive for this sequence; samples from other tumors and normal tissues were negative. The sequenced PCR products indicated that CTVT from Taiwan and other countries exhibited over 98% sequence homology. This reconfirms that, worldwide, all CTVT cells are very similar.