Shifts in bovine CD4(+) subpopulations increase T-helper-2 compared with T-helper-1 effector cells during the postpartum period

This study determined the cytokine profile of CD4(+) T-helper cells to eluc idate the specific CD4(+) T-helper phenotype during the postpartum period. Peripheral blood mononuclear cells were isolated from cows during periods o f increased susceptibility (3 d postpartum, n = 7) and decreased susceptibi lity (mid- to late lactation, n = 6) to mastitis. Isolated mononuclear cell s were magnetically separated into CD4(+)-enriched or CD4(+)-depleted popul ations using specific bovine monoclonal antibodies and were confirmed to be enriched or depleted by flow cytometric analysis. T-helper-1 and T-helper- 2 subpopulations were distinguished by cytokine profiles, at both the molec ular and protein level, by competitive quantitative reverse transcriptase-p olymerase chain reaction and specific bioassays, respectively. The CD4(+)-e nriched cultures isolated postpartum had enhanced interleukin-4 and interle ukin-10 mRNA transcript expression; cultures isolated during the mid- to la te lactating period had enhanced interleukin-a mRNA transcripts. Depletion of CD4(+) lymphocytes decreased, and enrichment of CD4(+) lymphocytes incre ased interferon-gamma transcripts in cultures isolated from mid- to late la ctation cows. Interferon-gamma and interleukin-2 bioassays revealed that cy tokine secretion paralleled mRNA transcript levels. These data suggest that CD4(+) lymphocytes act predominantly as T-helper-2 compared with T-helper- 1 within 3 d after calving. Alterations in the T-helper-1 and T-helper-2 re sponses, and therefore the repertoire of cytokines produced, may be an unde rlying reason for diminished host immune response during the postpartum per iod.