Constitutive secretion of interleukin 1 by human monocytes

The constitutive and lipopolysaccharide (LPS)-induced secretion of interleukin 1 (IL 1) by cultured human monocytes and macrophages has been studied. Both freshly obtained monocytes and their culture-derived macrophages were induced by LPS to secrete similar amounts of IL 1. Such induction, however, was accompanied by the secretion of dialyzed inhibitory activity. Constitutive secretion of IL 1 was detected in concentrated supernatants of monocyte cultures. The factor obtained constitutively did not manifest significant inhibitory activity. A method is described for the recovery of IL 1-containing supernatants in serum- and other stimulant-free medium. The biological activities of the constitutively secreted IL 1 were similar to the LPS-induced activities. The constitutive secretion of IL 1 was not equally distributed in the entire monocyte population. We found that a small fraction of loosely adherent monocytes secreted higher amounts of IL 1 than the strongly adherent monocytes. However, the property of higher secretion of IL 1 was not stable and disappeared following monocyte cultivation. Thus, constitutive activity of IL 1 could be recovered either by concentrating the culture supernatants or by enriching a subset of monocytes with higher IL 1 activity.

Antigen presentation and regulatory functions of human monocytes in the in vitro response of lymphocytes against purified protein derivative of tuberculin (PPD)

Monocyte functions in the primary and secondary proliferative responses of human lymphocytes against purified protein derivative of tuberculin (PPD) have been studied. By applying the antigens either directly to the responding cells or on antigen-treated autologous monocytes, it was possible to distinguish between two different monocyte functions: antigen presentation and regulation. Their helper function in lymphocyte proliferation was found in cell-free supernatants of autologous and allogeneic monocytes and was expressed better in the secondary rather than in the primary responses. The antigen-presenting function of monocytes, however, was found to be more substantial in the primary response of lymphocytes. These results suggest that macrophage dependency of certain immune functions should be considered in regard to the various functions of macrophages, since at least quantitative differences for each of the macrophage functions were found in the primary and secondary proliferative responses.

Characterization of human lymphocytes which proliferate "spontaneously" in vitro

Human peripheral blood lymphocytes proliferate "spontaneously" in vitro following the reduction in the proportion of monocytes in culture. This cell proliferation, which takes place in the absence of any extrinsic antigenic stimulation, was found to reside in a small fraction of a non-T non-B cell population which was also Fc receptor-negative. Concomitant with the in vitro proliferation of the monocyte-depleted cells, an increase in the proportion of E rosette-forming cells was observed. Hence, in addition to the regulation of spontaneous proliferation of lymphocytes, it is suggested that monocytes may also be involved in the regulation of the proportion of T cells or in expression of the E-rosetting marker.

In vitro proliferation of macrophage depleted human peripheral blood lymphocytes

The incorporation of thymidine by normal human peripheral blood lymphocytes was tested in vitro following various culture conditions. A significant increase of thymidine uptake was observed in cultures depleted of plastic adherent, nylon wook adherent, or phagocytic cells. This proliferative activity occurred in the presence of various sera but was not due to a blastogenic response to a foreign protein, since it was also observed when autologous plasma was the only source of protein in the culture medium. The similarities and differences between this 'spontaneous' proliferative phenomenon and other blastogenic responses which are regulated by macrophages are discussed.