Delayed-type hypersensitivity, contact sensitivity, and phytohemagglutinin skin-test responses of heat- and cold-stressed calves.

Three-week-old Holstein bull calves were used to investigate the effect of a 2-week chronic heat (35 C) or cold (-5 C) exposure on delayed-type hypersensitivity (DTH) reactions to purified protein derivative after sensitization with heat-killed Mycobacterium tuberculosis, contact sensitivity (CS) reactions to 1-fluoro-2,4-dinitrobenzene, and phytohemagglutinin (PHA) skin tests. Heat exposure reduced expression of DTH reactions by 42% and CS reactions by 38% at 24 hours after elicitation of the responses. The PHA-induced skin tests were not affected after 1 week of heat exposure, but this reaction was reduced by 20% after 2 weeks of heat exposure. The immune response of calves exposed to cold air temperatures was more complex. Cold exposure suppressed CS reactions by 39% at the end of both the 1st and 2nd weeks. The PHA response was reduced by 39% after 2 weeks of cold exposure. The DTH response depended on duration of cold exposure. The DTH reaction was increased by 42% after 1 week, but was reduced by 14% after 2 weeks. These data are consistent with the hypothesis that environmental stressors alter host resistance by affecting the immune system. Furthermore, these stress-induced changes in immune events depend on the type of immune response, the nature of the environmental stressor, and the length of time that calves are exposed to the stressor.