Significance of serum factors in the stimulation of human umbilical cord and fetal lymphocytes by soluble protein A from Staphylococcus aureus

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Abstract
Human umbilical cord and fetal lymphocytes were cultured in the presence of various sera [AB serum, fetal calf serum (FCS) and gammaglobulin‐free FCS] and soluble protein A from Staphylococcus aureus (SpA). Dose response studies showed that SpA in a final concentration of 100 μg/ml stimulated moderately cord blood lymphocytes. SpA‐induced DNA synthesis was significantly higher when cord lymphocytes were cultured with FCS than with AB serum or gammaglobulin‐free FCS. After 6 days' culture, even SpA without serum became a potent mitogen for these cells. The peak values for incorporation of thymidine into cord lymphocytes depended on the concentration of SpA and the serum used for culture. However, fetal splenocytes, thymocytes and peripheral lymphocytes reacted more avidly with SpA in cultures containing AB serum than FCS. Furthermore, serum‐free SpA cultures did not result in any activation of fetal lymphocytes. Regardless of whether cord blood lymphocytes were cultured with AB serum or FCS, both T and B subpopulations were stimulated. In contrast to fetal cells, the response of cord cells was stronger with FCS, and the peak values were shifted to later culture days.In conclusion, SpA acts as a mitogen both on T and B cells in early fetuses as well as in the newborn. Serum factors significantly influence the strength and kinetics of the mitogenic response.