The requirement of light chain for the surface deposition of the heavy chain of immunoglobulin M.

P E Mains,C H Sibley

doi:10.1016/s0021-9258(18)32532-8

Abstract

The murine tumor line 70Z/3 resembles a pre-B lymphocyte in containing the heavy chain of IgM (mu) as a cytoplasmic protein in the apparent absence of light chain (L). However, these cells can be induced by lipopolysaccharide to differentiate into a B lymphocyte-like state, containing mu2L2 tetramers as membrane-bound molecules. This is a accompanied by an increase in mu synthesis, the acquisition of complex carbohydrate by mu, and the induction of L chain. We wished to determine which of these events is critical for membrane deposition of mu. We found that uninduced 70Z/3 cells, as well as lipopolysaccharide-uninducible variants, contained a low, constitutive level of membrane bound mu, all of which was found as mu2L2. Dextran sulfate, another inducing agent, apparently caused a redistribution of this pre-existing surface mu without altering the pattern of mu synthesis or processing. One lipopolysaccharide-uninducible variant showed a small subset of surface mu-positive cells, and the proportion of these cells increased with a prolonged induction period. The increase in mu synthesis was nearly normal, but mu did not acquire complex carbohydrate. However, the delayed appearance of surface mu-positive cells was paralleled by a delayed increase in L chain, which occurred only in those cells with mu on their membrane. We concluded that L chain signals the transport of mu to the cell surface.

Highlights

Phocyte in containig the heavy chain ofIgM &) as a The earliest cell identified as being part of the B lymphocyte cytoplasmic protein in the apparent absence of light lineage is the pre-B cell, which is found in the fetal liver or chain (L)
The which was found as p2L2.Dextran sulfate, another in- different COOH termini result from a change in transcription ducing agent, apparently caused a redistributthioisn ooff the gene and/or processing of the nuclear RNA, resulting pre-existingsurface p without altering the patteronf p in alternate 3’ ends of the ps and pm mRNAs [13,14,15,16]
The in- internal p of the pre-B stage to themembrane-bound p of the crease inp synthesis was nearly normal, butp did not B lymphocyte, in an attempt tdoefinethe signal(s)responsible acquire complex carbohydrate. The delayed for this transition. appearance of surface p-positive cells was paralleled The induction of L chain is correlated with the pre-B to B by a delayed increase inL chain, which occurred only cell transition; Bcells whichdisplay high levelsof mIgM in those cells with p on their membrane.We concluded synthesize L chain, while pre-B cells with only cytoplasmic p that L chain signalsthe transporot f p to the cell surfaced. o not

Summary

Recipient of an American Cancer Society Faculty Research

We have found that uninduced cells, as well as lyzed on a CytofluorgrafSystem 50H andmodel 2150 computer uninduciblevariants,appearedtohave a low, constitutive (Ortho Diagnostic Systems, Westwood MA)as previously described level of membrane-bound p , and these externapl chains were [27]

RESULTS

A B ABCDEFGH

DISCUSSION