The lymphocyte surface. III. Function of Fc receptor, C'3 receptor and surface Ig bearing lymphocytes: identification of a radioresistant B cell

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Abstract
Rat thoracic duct lymphocytes (TDL) were depleted of Fc receptor (FcRL), C'3 receptor (CRL) or surface Ig bearing (IgL) lymphocytes as described in the preceding paper (Parish & Hayward 1974b, part II). The FcRL, CRL and IgL populations were also recovered in pure form and their ability to transfer antibody responsiveness to irradiated recipients was assessed. It was found that TDL from rats primed to DNP, when depleted of IgL, lost their capacity to transfer a secondary 7S antibody response to DNP; in contrast, depletion of FcRL did not affect the 7S response. CRL depletion eliminated the transferred primary 7S antibody response to polymerized flagellin and also reduced but did not eliminate the secondary 7S antibody response to DNP. Cells which are Ig+ CR+ appear to be the main source of secondary 7S precursors in the rat but Ig+ CR- cells can also, under certain circumstances, serve the same function. CRL, IgL and FcRL purified from DNP-primed TDL were unable to transfer secondary responsiveness to DNP. However, the addition of CRL or IgL to TDL depleted of these subpopulations resulted in a reconstitution of the secondary 7S antibody response. By using cytotoxic alloantisera CRL were identified as 7S antibody precursors. In order to mount a 7S antibody response to DNP, CRLs required the collaboration of non-CRLs, the CRL population containing the 7S precursors and the non-CRL population contributing helper (T) cells. Removal of either CRL, IgL or FcRL from TDL had no effect on the 19S anti-DNP response which arose in the irradiated recipients. The same result was obtained whether the 19S and 7S antibodies were characterized by their 2ME sensitivity, by their sedimentation behaviour on sucrose gradients or by their expression of direct and indirect PFC. However, no conclusions could be drawn from these observations about the nature of 19S precursor cells because it was found that virtually all the cells producing 19S anti-DNP antibody originated from the irradiated hosts, indicating that radioresistant 19S precursors exist in the rat. On some occasions radioresistant 7S precursors were also detected. To be activated by antigen both radioresistant populations require the presence of primed helper (T) cells. These results emphasize the extreme caution required in interpreting experiments that involve cell transfers into irradiated recipients.