Abstract
Studies comparing in vivo and in vitro functional capacities of leukocytes from non-parturient and periparturient dairy cows have provided substantial evidence that systemic and local mammary immune defenses are deficient around parturition. This evidence has lead to the reasonable hypothesis that immune deficiency underlies the heightened mastitis susceptibility of periparturient cows. Nutrition and vaccine studies substantiate this hypothesis, showing that dietary antioxidant supplementation and rigorous immunization regimes can bolster innate and humoral immunity to the point that mastitis severity and time for return to normal milk production are reduced. However, completely effective resolution of this significant production disease has not been achieved because so little is understood about its complex etiology. In particular, we possess almost no knowledge of how or why immune cells responding to parturient physiology end up with deficient functional capacities. Fluctuations in reproductive steroid hormones and chronic shifts in neuroendocrine hormones with roles in nutrient partitioning and appetite control may affect the expression of critical leukocyte genes in periparturient dairy cows. A thorough understanding of leukocyte biology during periparturition would seem a critical goal for future development of effective mastitis prevention strategies. Recently, our group has begun to use cDNA microarray technology to explore bovine leukocyte RNA for global gene expression changes occurring around parturition. We are working within the context of a hypothesis that the physiology of parturition negatively affects expression of critical genes in blood leukocytes. In the current study we initiated hypothesis testing using leukocyte RNA from a high producing Holstein cow collected at 14 days prepartum and 6 hours postpartum to interrogate a cDNA microarray spotted with > 700 cDNAs representing unique bovine leukocyte genes. This analysis revealed 18 genes with > or = 1.2-fold higher expression 14 days prepartum than 6 hours postpartum. BLASTN analysis of these genes revealed only one that can be considered a classical immune response gene. All other repressed genes were either unknown or putatively identified as encoding key proteins involved in normal growth and metabolism of cells. Given the critical roles of these repressed genes in normal cell functions, we may have identified good candidates to pursue with respect to periparturient immunosuppression and mastitis susceptibility.
Highlights
Despite rigorous management practices aimed at environmental cleanliness, good nutrition, and vaccination, mastitis remains a problem in high producing dairy cows during periparturition (Eberhart 1984, 1986, Erskine et al 1988, Gonzalez et al 1988, Hogan et al 1989, Gonzalez et al 1990, Hoblet 1991, Erskine & Bartlett 1995, National Mastitis Council 1996)
BLASTN results in Table 1 showed that the bovine total leukocyte (BOTL) cDNA sequences for the 6 repressed genes in Fig. 5 were either unknown (9_G07, 4XD09R) or had high homology with molecules involved in DNA binding and transcription (6XG09R, 8-B07) and signal transduction (8_F09)
BLASTN results in Table 1 showed that the BOTL cDNA sequences for the 8 repressed genes in Fig. 6 were either unknown (8_B05, 10_A07) or had high homology with a variety of molecules involved in hormone binding (12_B09), cell growth (12_B06), leukocyte extravasation (6XC10R), and cell signaling (4XD08R, 3XA10R)
Summary
Despite rigorous management practices aimed at environmental cleanliness, good nutrition, and vaccination, mastitis remains a problem in high producing dairy cows during periparturition (Eberhart 1984, 1986, Erskine et al 1988, Gonzalez et al 1988, Hogan et al 1989, Gonzalez et al 1990, Hoblet 1991, Erskine & Bartlett 1995, National Mastitis Council 1996). Selection against mastitis susceptibility is possible (Lindé 1982, Jensen et al 1981, Lindé 1982, Skjervold 1982, McDnaiel 1984, Solbu 1984, Uribe et al 1995) Research in this area has a long history and has been focused primarily on determining appropriate traits or markers for genetic selection (e.g., Lie 1977; Lindström & Syväjärvi 1978, Lie 1979, Lie & Solbu 1981, Almlid 1981, Lie et al 1982, Mazengera et al 1985, Lie et al 1986, Lewin 1989, Strandberg & Shook 1989, Vage et al 1992, Mejdell et al, 1994, Shook 1993, Shook & Schutz 1994, Detilleux et al 1994, 1995a, Vecht et al 1985, Dietz et al 1997, Kelm et al 1997, Sharif et al 1998, 1999, Wagter et al 2000). This paper focuses on our first cDNA microarray analysis of global gene expression changes that occur in bovine blood leukocytes around parturition
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